scholarly journals Detection and characterization of a 3' untranslated region ribonucleoprotein complex associated with human alpha-globin mRNA stability.

1995 ◽  
Vol 15 (3) ◽  
pp. 1769-1777 ◽  
Author(s):  
X Wang ◽  
M Kiledjian ◽  
I M Weiss ◽  
S A Liebhaber
Keyword(s):  
Complex Formation ◽  
Mrna Stability ◽  
Untranslated Region ◽  
Binding Protein ◽  
Erythroid Cell ◽  
Globin Mrna ◽  
Rnp Complex ◽  
Alpha Globin

The highly stable nature of globin mRNA is of central importance to erythroid cell differentiation. We have previously identified cytidine-rich (C-rich) segments in the human alpha-globin mRNA 3' untranslated region (alpha-3'UTR) which are critical in the maintenance of mRNA stability in transfected erythroid cells. In the present studies, we have detected trans-acting factors which interact with these cis elements to mediate this stabilizing function. A sequence-specific ribonucleoprotein (RNP) complex is assembled after incubation of the alpha-3'UTR with a variety of cytosolic extracts. This so-called alpha-complex is sequence specific and is not formed on the 3'UTR of either beta-globin or growth hormone mRNAs. Furthermore, base substitutions within the C-rich stretches which destabilize alpha-globin mRNA in vivo result in a parallel disruption of the alpha-complex in vitro. Competition studies with a series of homoribopolymers reveals a striking sensitivity of alpha-complex formation to poly(C), suggesting the presence of a poly(C)-binding activity within the alpha-complex. Three predominant proteins are isolated by alpha-3'UTR affinity chromatography. One of these binds directly to poly(C). This cytosolic poly(C)-binding protein is distinct from previously described nuclear poly(C)-binding heterogeneous nuclear RNPs and is necessary but not sufficient for alpha-complex formation. These data suggest that a messenger RNP complex formed by interaction of defined segments within the alpha-3'UTR with a limited number of cytosolic proteins, including a potentially novel poly(C)-binding protein, is of functional importance in establishing high-level stability of alpha-globin mRNA.

scholarly journals Identification of AUF1 (heterogeneous nuclear ribonucleoprotein D) as a component of the alpha-globin mRNA stability complex.

1997 ◽  
Vol 17 (8) ◽  
pp. 4870-4876 ◽  
Author(s):  
M Kiledjian ◽  
C T DeMaria ◽  
G Brewer ◽  
K Novick
Keyword(s):  
Mrna Stability ◽  
Binding Activity ◽  
Mrna Turnover ◽  
Globin Mrna ◽  
Hnrnp D ◽  
Rnp Complex ◽  
Specific Accumulation ◽  
Alpha Globin

mRNA turnover is an important regulatory component of gene expression and is significantly influenced by ribonucleoprotein (RNP) complexes which form on the mRNA. Studies of human alpha-globin mRNA stability have identified a specific RNP complex (alpha-complex) which forms on the 3' untranslated region (3'UTR) of the mRNA and appears to regulate the erythrocyte-specific accumulation of alpha-globin mRNA. One of the protein activities in this multiprotein complex is a poly(C)-binding activity which consists of two proteins, alphaCP1 and alphaCP2. Neither of these proteins, individually or as a pair, can bind the alpha-globin 3'UTR unless they are complexed with the remaining non-poly(C) binding proteins of the alpha-complex. With the yeast two-hybrid screen, a second alpha-complex protein was identified. This protein is a member of the previously identified A+U-rich (ARE) binding/degradation factor (AUF1) family of proteins, which are also known as the heterogeneous nuclear RNP (hnRNP) D proteins. We refer to these proteins as AUF1/hnRNP-D. Thus, a protein implicated in ARE-mediated mRNA decay is also an integral component of the mRNA stabilizing alpha-complex. The interaction of AUF1/hnRNP-D is more efficient with alphaCP1 relative to alphaCP2 both in vitro and in vivo, suggesting that the alpha-complex might be dynamic rather than a fixed complex. AUF1/hnRNP-D could, therefore, be a general mRNA turnover factor involved in both stabilization and decay of mRNA.

scholarly journals A Nucleolin-Binding 3′ Untranslated Region Element Stabilizes β-Globin mRNA In Vivo

2006 ◽  
Vol 26 (6) ◽  
pp. 2419-2429 ◽  
Author(s):  
Yong Jiang ◽  
Xiang-Sheng Xu ◽  
J. Eric Russell
Keyword(s):  
Mrna Stability ◽  
Untranslated Region ◽  
Rna Binding ◽  
Critical Role ◽  
Specific Interaction ◽  
Globin Mrna ◽  
Intact Cells ◽  
Normal Expression

ABSTRACT The normal expression of human β globin is critically dependent upon the constitutively high stability of its encoding mRNA. Unlike with α-globin mRNA, the specific cis-acting determinants and trans-acting factors that participate in stabilizing β-globin mRNA are poorly described. The current work uses a linker-scanning strategy to identify a previously unknown determinant of mRNA stability within the β-globin 3′ untranslated region (3′UTR). The new determinant is positioned on an mRNA half-stem opposite a pyrimidine-rich sequence targeted by αCP/hnRNP-E, a factor that plays a critical role in stabilizing human α-globin mRNA. Mutations within the new determinant destabilize β-globin mRNA in intact cells while also ablating its 3′UTR-specific interaction with the polyfunctional RNA-binding factor nucleolin. We speculate that 3′UTR-bound nucleolin enhances mRNA stability by optimizing αCP access to its functional binding site. This model is favored by in vitro evidence that αCP binding is enhanced both by cis-acting stem-destabilizing mutations and by the trans-acting effects of supplemental nucleolin. These studies suggest a mechanism for β-globin mRNA stability that is related to, but distinct from, the mechanism that stabilizes human α-globin mRNA.

scholarly journals The Poly(A)-Binding Protein and an mRNA Stability Protein Jointly Regulate an Endoribonuclease Activity

2000 ◽  
Vol 20 (17) ◽  
pp. 6334-6341 ◽  
Author(s):  
Zuoren Wang ◽  
Megerditch Kiledjian
Keyword(s):  
Mrna Stability ◽  
Binding Protein ◽  
The Body ◽  
Erythroid Cell ◽  
Target Sequence ◽  
Globin Mrna ◽  
Mobility Shift ◽  
Cytosolic Extract ◽  
Electrophoretic Mobility Shift Assays

ABSTRACT We previously identified a sequence-specific erythroid cell-enriched endoribonuclease (ErEN) activity involved in the turnover of the stable α-globin mRNA. We now demonstrate that ErEN activity is regulated by the poly(A) tail. The unadenylated α-globin 3′ untranslated region (3′UTR) was an efficient substrate for ErEN cleavage, while the polyadenylated 3′UTR was inefficiently cleaved in an in vitro decay assay. The influence of the poly(A) tail was mediated through the poly(A)-binding protein (PABP) bound to the poly(A) tail, which can inhibit ErEN activity. ErEN cleavage of an adenylated α-globin 3′UTR was accentuated upon depletion of PABP from the cytosolic extract, while addition of recombinant PABP reestablished the inhibition of endoribonuclease cleavage. PABP inhibited ErEN activity indirectly through an interaction with the αCP mRNA stability protein. Sequestration of αCP resulted in an increase of ErEN cleavage activity, regardless of the polyadenylation state of the RNA. Using electrophoretic mobility shift assays, PABP was shown to enhance the binding efficiency of αCP to the α-globin 3′UTR, which in turn protected the ErEN target sequence. Conversely, the binding of PABP to the poly(A) tail was also augmented by αCP, implying that a stable higher-order structural network is involved in stabilization of the α-globin mRNA. Upon deadenylation, the interaction of PABP with αCP would be disrupted, rendering the α-globin 3′UTR more susceptible to endoribonuclease cleavage. The data demonstrated a specific role for PABP in protecting the body of an mRNA in addition to demonstrating PABP's well-characterized effect of stabilizing the poly(A) tail.

scholarly journals The 3′ Untranslated Region Complex Involved in Stabilization of Human α-globin mRNA Assembles in the Nucleus and Serves an Independent Role as a Splice Enhancer

2007 ◽  
Vol 27 (9) ◽  
pp. 3290-3302 ◽  
Author(s):  
Xinjun Ji ◽  
Jian Kong ◽  
Russ P. Carstens ◽  
Stephen A. Liebhaber
Keyword(s):  
Untranslated Region ◽  
Rna Binding ◽  
Protein Complexes ◽  
Binding Protein ◽  
Splice Enhancer ◽  
Globin Mrna ◽  
Nuclear Assembly ◽  
General Importance

ABSTRACT Posttranscriptional controls, mediated primarily by RNA-protein complexes, have the potential to alter multiple steps in RNA processing and function. Human α-globin mRNA is bound at a C-rich motif in the 3′ untranslated region (3′UTR) by the KH domain protein α-globin poly(C)-binding protein (αCP). This “α-complex” is essential to cytoplasmic stability of α-globin mRNA in erythroid cells. Here we report that the 3′UTR α-complex also serves an independent nuclear role as a splice enhancer. Consistent with this role, we find that αCP binds α-globin transcripts prior to splicing. Surprisingly, this binding occurs at C-rich sites within intron I as well as at the 3′UTR C-rich determinant. The intronic and 3′UTR αCP complexes appear to have distinct effects on splicing. While intron I complexes repress intron I excision, the 3′UTR complex enhances splicing of the full-length transcript both in vivo and in vitro. In addition to its importance to splicing, nuclear assembly of the 3′UTR αCP complex may serve to “prepackage” α-globin mRNA with its stabilizing complex prior to cytoplasmic export. Linking nuclear and cytoplasmic controls by the action of a particular RNA-binding protein, as reported here, may represent a modality of general importance in eukaryotic gene regulation.

scholarly journals A U-Rich Element in the 5′ Untranslated Region Is Necessary for the Translation of p27 mRNA

2000 ◽  
Vol 20 (16) ◽  
pp. 5947-5959 ◽  
Author(s):  
S. Sean Millard ◽  
Anxo Vidal ◽  
Maurice Markus ◽  
Andrew Koff
Keyword(s):  
Cell Cycle ◽  
Mrna Stability ◽  
Untranslated Region ◽  
Mrna Processing ◽  
Differentiated Cells ◽  
Specific Subset ◽  
Number Of Factors ◽  
Rnp Complex ◽  
Cycle Dependent

ABSTRACT Increased translation of p27 mRNA correlates with withdrawal of cells from the cell cycle. This raised the possibility that antimitogenic signals might mediate their effects on p27 expression by altering complexes that formed on p27 mRNA, regulating its translation. In this report, we identify a U-rich sequence in the 5′ untranslated region (5′UTR) of p27 mRNA that is necessary for efficient translation in proliferating and nonproliferating cells. We show that a number of factors bind to the 5′UTR in vitro in a manner dependent on the U-rich element, and their availability in the cytosol is controlled in a growth- and cell cycle-dependent fashion. One of these factors is HuR, a protein previously implicated in mRNA stability, transport, and translation. Another is hnRNP C1 and C2, proteins implicated in mRNA processing and the translation of a specific subset of mRNAs expressed in differentiated cells. In lovastatin-treated MDA468 cells, the mobility of the associated hnRNP C1 and C2 proteins changed, and this correlated with increased p27 expression. Together, these data suggest that the U-rich dependent RNP complex on the 5′UTR may regulate the translation of p27 mRNA and may be a target of antimitogenic signals.

Auf-1 and YB-1 Independently Regulate β-Globin mRNA Stability Through Interaction with Poly(A) Binding Protein

Blood ◽  
2012 ◽  
Vol 120 (21) ◽  
pp. 1020-1020
Author(s):  
Sebastiaan van Zalen ◽  
Alyssa A Lombardi ◽  
Grace R Jeschke ◽  
Elizabeth O Hexner ◽  
J. Eric Russell
Keyword(s):  
Mrna Stability ◽  
Half Life ◽  
High Stability ◽  
Binding Protein ◽  
K562 Cells ◽  
Erythroid Progenitors ◽  
Globin Mrna ◽  
Hematopoietic Stem ◽  
Knock Down

Abstract Abstract 1020 The normal expression of Hb A in humans requires the high-level stability of α - and β-globin mRNAs in both transcriptionally active and transcriptionally silenced erythroid progenitors. In contrast to α -globin–whose stability is known to be enhanced by an mRNA-protein (mRNP) complex that assembles on a specific pyrimidine-rich track within its 3'UTR–the structure(s) and mechanism(s) that underlie the high stability of human β-globin mRNA remain poorly defined. We recently identified two RNA-binding proteins, AUF-1 and YB-1, that regulate levels of β-globin mRNA in erythroid progenitors by assembling a cytoplasm-restricted mRNP 'β-complex' on its 3'UTR. The function of the β-complex was predicted by in vitro analyses that mapped its binding to a cis-acting determinant of β-globin mRNA stability, and by in vivo siRNA studies demonstrating that simultaneous knockdown of AUF-1 and YB-1 coordinately ablated the β-complex and coordinately reduced the accumulation of β-globin mRNA in K562 cells. The biological importance of the β-complex was subsequently confirmed in human hematopoietic stem cells, where shRNA-mediated knock-down of AUF-1 or YB-1 effected lower levels of β-globin mRNA in cells induced to the erythroid lineage, again implicating their participation in post-transcriptional mechanism(s) regulating the stability of β-globin mRNA. To unambiguously link β-complex activity to β-globin mRNA half-life, we conducted formal in vivo mRNA stability analyses in K562 cells using a β-globin mRNA-specific tetracycline-conditional transcriptional chase strategy. A derivative β-globin mRNA carrying a 5-nt substitution that totally disrupts β-complex assembly (βMut mRNA) displayed a lower half-life than wild-type β-globin mRNA (βWT mRNA), confirming the participation of the β-complex in post-transcriptional regulatory processes. Parallel poly(A) tail length analyses indicated a possible mechanism for this activity, revealing that the βMut mRNA had a shortened steady-state poly(A) tail that truncated faster than the poly(A) tail on βWT mRNA, suggesting a functional interaction between the β-complex and poly(A) tail-associated factors. This observation is fully consistent with the known importance of deadenylation to processes regulating the decay of heterologous mRNAs in several other experimental systems. Subsequent studies supported our model for β-complex/poly(A) tail interaction: electrophoretic gel mobility-shift analyses demonstrated that the β-complex readily assembles on polyadenylated β-globin 3'UTRs but not on corresponding deadenylated 3'UTRs, while RNA affinity capture experiments using K562 cytoplasmic extracts demonstrated that a polyadenylated βWT 3'UTR retains poly(A) binding protein (PABP), while a similar β-complex-deficient βMut 3'UTR fails to bind PABP. Ongoing co-immunoprecipation studies are expected to determine whether the β-complex and PABP are tethered by an interval of mRNA or, alternately, interact directly via a protein-protein interaction. Based upon our previous structural and functional analyses indicating that AUF-1 and YB-1 act redundantly to regulate the cytoplasmic level of β-globin mRNA, we are currently investigating the hypothesis that these two factors also display redundant interactions with the poly(A) tail and its trans-acting binding factors. Our initial RNA affinity analyses confirm this expectation, demonstrating that K562 extracts depleted of either AUF-1 or YB-1 (using an shRNA-knock-down strategy) both maintained the ability to assemble a β-complex as well as facilitate PABP binding to a the polyadenylated βWT 3'UTR. We are presently testing AUF-1 and YB-1 for corresponding functional redundancy (i.e., their abilities to independently induce βWT mRNA stability) using in vivo mRNA tethering experiments in which AUF-1 or YB-1 can be structurally modified to promote their independent interaction with the β-complex binding site. Altogether, these experiments demonstrate that the β-complex, through its component mRNA-binding factors AUF-1 and YB-1, effects the high stability of β-globin mRNA by interacting with PABP. A detailed structural and mechanistic description of this process will be invaluable to the design of novel therapeutics for patients with congenital disorders of β-globin gene expression. Disclosures: No relevant conflicts of interest to declare.

scholarly journals An mRNA Stability Complex Functions with Poly(A)-Binding Protein To Stabilize mRNA In Vitro

1999 ◽  
Vol 19 (7) ◽  
pp. 4552-4560 ◽  
Author(s):  
Zuoren Wang ◽  
Nancy Day ◽  
Panayiota Trifillis ◽  
Megerditch Kiledjian
Keyword(s):  
Mrna Stability ◽  
Binding Protein ◽  
Major Protein ◽  
Globin Mrna ◽  
Ideal System ◽  
Complex Functions ◽  
Cytosolic Extract ◽  
Protein Components ◽  
The Stability

ABSTRACT The stable globin mRNAs provide an ideal system for studying the mechanism governing mammalian mRNA turnover. α-Globin mRNA stability is dictated by sequences in the 3′ untranslated region (3′UTR) which form a specific ribonucleoprotein complex (α-complex) whose presence correlates with mRNA stability. One of the major protein components within this complex is a family of two polycytidylate-binding proteins, αCP1 and αCP2. Using an in vitro-transcribed and polyadenylated α-globin 3′UTR, we have devised an in vitro mRNA decay assay which reproduces the α-complex-dependent mRNA stability observed in cells. Incubation of the RNA with erythroleukemia K562 cytosolic extract results in deadenylation with distinct intermediates containing a periodicity of approximately 30 nucleotides, which is consistent with the binding of poly(A)-binding protein (PABP) monomers. Disruption of the α-complex by sequestration of αCP1 and αCP2 enhances deadenylation and decay of the mRNA, while reconstitution of the α-complex stabilizes the mRNA. Similarly, PABP is also essential for the stability of mRNA in vitro, since rapid deadenylation resulted upon its depletion. An RNA-dependent interaction between αCP1 and αCP2 with PABP suggests that the α-complex can directly interact with PABP. Therefore, the α-complex is an mRNA stability complex in vitro which could function at least in part by interacting with PABP.

scholarly journals Alpha 2-macroglobulin binds and inhibits activated protein C

Blood ◽  
1991 ◽  
Vol 78 (9) ◽  
pp. 2283-2290 ◽  
Author(s):  
H Hoogendoorn ◽  
CH Toh ◽  
ME Nesheim ◽  
AR Giles
Keyword(s):  
Complex Formation ◽  
Active Site ◽  
Metal Ion ◽  
Protein C ◽  
Binding Protein ◽  
Polyacrylamide Gel Electrophoresis ◽  
Sodium Dodecyl ◽  
High Molecular Weight Complex

In previous studies using a nonhuman primate model of Protein C (PC) activation in vivo, immunoblotting showed substantial amounts of activated PC (APC) in a high molecular weight complex with what was presumed to be a previously unrecognized APC binding protein. This APC complex can also be formed in citrated plasma in vitro. It is of low electrophoretic mobility, sodium dodecyl sulfate (SDS) stable, with an apparent Mr of 320 Kd. Its purification from human plasma was accomplished using barium citrate adsorption, sequential polyethylene glycol (PEG) precipitations, diethylaminoethyl sepharose chromatography, AcA-34 gel filtration, and zinc-chelate affinity chromatography. This was monitored by subjecting the fractions to nondenaturing polyacrylamide gel electrophoresis (PAGE), transfer to polyvinylidene-difluoride membranes, and probing with 125I-labeled human APC. The purified APC-binding protein was homogeneous by SDS-PAGE with an Mr of 275 Kd. Its identity as alpha 2-macroglobulin (alpha 2M) was demonstrated immunochemically. Complex formation between alpha 2M and APC was found to be almost completely inhibited by EDTA, but to a lesser extent by citrate. Complex formation could also be prevented by active site inhibition with D-Phenylalanyl-L-Prolyl-L-Arginine- Chloromethyl Ketone (PPACK) or pretreatment of alpha 2M with methylamine. Incubation of APC (33 nmol/L) with alpha 2M (1 mumol/L) resulted in time-dependent inhibition of APC anticoagulant activity when measured using an activated partial thromboplastin time based APC assay. These data show that alpha 2M binds and inhibits APC in vitro and the interaction is both metal-ion and active-site dependent, requiring functionally intact alpha 2M. As the complexes formed in vitro comigrate electrophoretically with those observed in vivo after PC activation, it is suggested that alpha 2M is a physiologically relevant inhibitor involved in the processing of APC in vivo.

Nucleolin-Mediated Stabilization of Human β-Globin mRNA.

Blood ◽  
2005 ◽  
Vol 106 (11) ◽  
pp. 524-524 ◽  
Author(s):  
J. Eric Russell ◽  
Xiang-Sheng Xu ◽  
Yong Jiang
Keyword(s):  
Binding Site ◽  
Mrna Stability ◽  
Globin Gene ◽  
Full Length ◽  
Critical Importance ◽  
Globin Mrna ◽  
Left Half ◽  
Affinity Enrichment

Abstract The normal expression of human β globin is critically dependent upon the high stability of its encoding mRNA. The mechanism that protects β-globin mRNA from premature degradation--including the positions of cis-acting stability determinants, the identities of relevant trans-acting factors, and the processes through which they interact--are poorly understood. We have designed and executed a series of experiments that detail the critical importance of the 3′UTR to the high constitutive stability of β-globin mRNA. To identify mRNA-stability determinants in this region, we constructed a wild-type β-globin gene (βWT), as well as 17 derivative genes containing site-specific 3′UTR hexanucleotide substitutions (βMUT1-βMUT17), each under the transcriptional control of a tetracycline-response element (TRE). In cultured cells that express a corresponding transcriptional transactivator, the expression of TRE-linked βWT and βMUT genes can be rapidly silenced by adding tetracycline to the culture medium, permitting the stabilities of the cognate mRNAs to be established using a transcriptional chase approach. Two of the 17 mRNAs, carrying adjacent hexanucleotide substitutions (βMUT12 and βMUT13), were destabilized in intact HeLa cells, identifying a sequence that is critical to β-globin mRNA stability. Three potentially important trans-acting factors that bind to this region were subsequently isolated using an in vitro affinity-enrichment method. One of the proteins was unequivocally identified by mass spec analysis to be nucleolin, a ubiquitous nuclear-cytoplasmic factor that exhibits RNA helicase activity and is reported to stabilize several non-erythroid mRNAs. A link between this factor and β-globin mRNA stability was provided by in vitro studies demonstrating that purified nucleolin binds tightly to the βWT 3′UTR but poorly to both βMUT12 and βMUT13 3′UTRs. This result was validated by RNA-immunoprecipitation (RIP) analyses confirming a strong interaction between nucleolin and βWT mRNA in intact cells that is fully ablated by MUT12 or MUT13 hexanucleotide substitutions. The critical importance of nucleolin binding to the stability of β-globin mRNA may relate to a stem-and-loop motif within its 3′UTR that is predicted by mRNA-folding algorithms. This structure contains the nucleolin-binding site on its right half-stem, opposite a putative binding site for αCP, a 34 kDa factor that stabilizes α-globin mRNA, on the left half-stem. Surprisingly, recombinant αCP displays a low affinity for the full-length β-globin 3′UTR, while binding avidly to the isolated left half-stem as well as to full-length β-globin 3′UTRs that contain stem-disrupting mutations. These results indicate that high-order structures within the β-globin 3′UTR, if permitted to form, may interfere with αCP function in vivo. Based upon our studies, we suggest that nucleolin binding is required to relax a highly stable stem-and-loop motif within the β-globin 3′UTR, exposing a functional binding site for the mRNA-stabilizing factor αCP. Thus, we identify a cis-element and a specific trans-acting factor that participate in stabilizing β-globin mRNA, and suggest a mechanism through which they are likely to act in vivo. The full elucidation of this process will clearly benefit the design of therapeutic transgenes for individuals with β-globin gene defects, and may additionally facilitate the conception of novel therapies intended to differentially regulate the stabilities of βS- and γ-globin mRNAs in individuals with sickle cell disease.

scholarly journals Structural and Functional Analysis of an mRNP Complex That Mediates the High Stability of Human β-Globin mRNA

2001 ◽  
Vol 21 (17) ◽  
pp. 5879-5888 ◽  
Author(s):  
Jia Yu ◽  
J. Eric Russell
Keyword(s):  
Mrna Stability ◽  
Rna Binding ◽  
Assembly Sequence ◽  
Regulatory Pathway ◽  
Globin Mrna ◽  
Mrnp Complex ◽  
The Stability ◽  
High Level

ABSTRACT Human globins are encoded by mRNAs exhibiting high stabilities in transcriptionally silenced erythrocyte progenitors. Unlike α-globin mRNA, whose stability is enhanced by assembly of a specific messenger RNP (mRNP) α complex on its 3′ untranslated region (UTR), neither the structure(s) nor the mechanism(s) that effects the high-level stability of human β-globin mRNA has been identified. The present work describes an mRNP complex assembling on the 3′ UTR of the β-globin mRNA that exhibits many of the properties of the stability-enhancing α complex. The β-globin mRNP complex is shown to contain one or more factors homologous to αCP, a 39-kDa RNA-binding protein that is integral to α-complex assembly. Sequence analysis implicates a specific 14-nucleotide pyrimidine-rich track within its 3′ UTR as the site of β-globin mRNP assembly. The importance of this track to mRNA stability is subsequently verified in vivo using mice expressing human β-globin transgenes that contain informative mutations in this region. In combination, the in vitro and in vivo analyses indicate that the high stabilities of the α- and β-globin mRNAs are maintained through related mRNP complexes that may share a common regulatory pathway.

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