scholarly journals Synthesis and turnover of ribulose biphosphate carboxylase and of its subunits during the cell cycle of Chlamydomonas reinhardtii.

1975 ◽  
Vol 64 (3) ◽  
pp. 572-585 ◽  
Author(s):  
V Iwanij ◽  
N H Chua ◽  
P Siekevitz
Keyword(s):  
Cell Cycle ◽  
Protein Synthesis ◽  
Enzymatic Activity ◽  
Chlamydomonas Reinhardtii ◽  
De Novo ◽  
Large Subunit ◽  
Dark Phase ◽  
Detectable Rate ◽  
De Novo Protein Synthesis ◽  
Slow Turnover

The chloroplast enzyme ribulose-1,5-bisphosphate (Ru-1,5-P2) carboxylase (EC 4.1 1.39) is made up ot two nonidentical subunits, one synthesized in the chloroplast and the other outside. Both of these subunits of the assembled enzyme are synthesized in a stepwise manner during the synchronous cell cycle of the green alga Chlamydomonas reinhardtii. The activity of this enzyme increases in the light and this increase is due to de novo protein synthesis as shown by the measurement of the amount of protein and by the pulse incorporation of radioactive arginine in the 18S enzyme peak in linear sucrose density gradients. During the dark phase of the cell cycle, there is little change in the enzymatic activity as well as in the amount of this enzyme. Pulse-labeling studies using radioactive arginine indicated that there is a slow but detectable rate of synthesis of the carboxylase and of its subunits in the dark. Ru-1,5-P2 carboxylase, prelabeled with radioactive arginine throughout the entire light period, shows a similarly slow rate of degradation in the following dark period. This slow turnover of the enzyme in the dark accounts for the steady levels of carboxylase protein and of enzymatic activity during this period. A wide variety of inhibitors of protein synthesis by 70S and 80S ribosomes abolished the incorporation of [3H]arginine into total Ru-1,5-P2 carboxylase during short-term incubation. These results suggest a tight-coordinated control of the biosynthesis of the small and large subunits of the enzyme. This stringent control is further substantiated by the finding that both subunits are synthesized in sychrony with each other, that the ratio of radioactivity of the small to the large subunit remains constant throughout the entire light-dark cycle, and that the rates of synthesis and of degradation of both subunits are similar to that of the assembled enzyme.

Flagellar regeneration in Chlamydomonas reinhardtii: evidence that cycloheximide pulses induce a delay in morphogenesis

1976 ◽  
Vol 20 (3) ◽  
pp. 639-654
Author(s):  
K.W. Farrell
Keyword(s):  
Protein Synthesis ◽  
Chlamydomonas Reinhardtii ◽  
De Novo ◽  
Full Length ◽  
Drug Inhibition ◽  
Flagellar Regeneration ◽  
De Novo Protein Synthesis ◽  
Half Length

The behaviour of a pool of flagellar precursors, assayed by the ability of cells to regenerate flagella in the absence of de novo protein synthesis, has been examined during organelle morphogenesis in the biflagellate alga Chlamydomonas. The results demonstrate that flagellar elongation can continue even when this pool is apparently empty and suggest that 2 sources of precursors are available to the regenerating flagella: those pre-existing in the cellular pool and those synthesized de novo. Further evidence for this was obtained by subjecting regenerating cells to pulses of cycloheximide. Cells exposed to this drug during the first 60 min post deflagellation formed only half-length (5-mum) flagella, whereas a pulse administered after this point allowed the formation of longer flagella and suggested that some de novo protein synthesis was required for the formation of full-length flagella, although it was not a prerequisite for the initiation of regeneration. In addition, it was found that, subsequent to the removal of the cycloheximide, flagellar regeneration did not recommence immediately, but was delayed for a period of approximately 45 min, irrespective of length of flagella formed prior to drug inhibition. The nature of this cycloheximide-induced delay is unclear and certain alternatives, based on the exhaustion of structural/regulatory components are considered. Although it is not possible to distinguish between these alternatives, tubulin is not the limiting component, since a pool of this protein is present when flagellar elongation is prevented by cycloheximide.

The HTLV receptor is an early T-cell activation marker whose expression requires de novo protein synthesis

Blood ◽  
2003 ◽  
Vol 101 (5) ◽  
pp. 1913-1918 ◽  
Author(s):  
Nicolas Manel ◽  
Sandrina Kinet ◽  
Jean-Luc Battini ◽  
Felix J. Kim ◽  
Naomi Taylor ◽  
...  
Keyword(s):  
Cell Cycle ◽  
Protein Synthesis ◽  
T Cell ◽  
T Lymphocytes ◽  
De Novo ◽  
Receptor Expression ◽  
Cell Leukemia Virus Type ◽  
Activation Marker ◽  
Cell Cycle Entry ◽  
De Novo Protein Synthesis

The human T-cell leukemia virus type 1 (HTLV) is the first isolated human retrovirus, but its receptor has yet to be identified, in part due to its ubiquitous expression. Here we report that quiescent CD4 and CD8 T lymphocytes do not express this receptor, as monitored with a soluble receptor-binding domain derived from the HTLV envelope. However, HTLV receptor is an early activation marker in neonatal and adult T lymphocytes, detected as early as 4 hours following T-cell–receptor (TCR) stimulation. This induced surface expression of the HTLV receptor requires de novo protein synthesis and results in a wide distribution on the surface of activated lymphocytes. Moreover, the distribution of the HTLV receptor is independent of TCR/CD3-capped membrane structures, as observed by confocal immunofluorescence microscopy. To determine whether HTLV receptor up-regulation specifically requires TCR-mediated signals or, alternatively, is dependent on more generalized cell cycle entry/proliferation signals, its expression was monitored in interleukin 7 (IL-7)–stimulated neonatal and adult T cells. Neonatal, but not adult, lymphocytes proliferate in response to IL-7 and HTLV receptor expression is restricted to the former population. Thus, HTLV receptor expression appears to be an early marker of cell cycle entry. Up-regulation of the HTLV receptor, via signals transmitted through the IL-7 cytokine receptor as well as the TCR, is likely to contribute to the mother-to-infant transmission and spreading of HTLV-1.

scholarly journals Chlamydomonas alpha-tubulin is posttranslationally modified in the flagella during flagellar assembly.

1983 ◽  
Vol 97 (1) ◽  
pp. 258-263 ◽  
Author(s):  
S W L'Hernault ◽  
J L Rosenbaum
Keyword(s):  
Protein Synthesis ◽  
Chlamydomonas Reinhardtii ◽  
Cell Body ◽  
Posttranslational Modification ◽  
De Novo ◽  
Alpha Tubulin ◽  
Flagellar Assembly ◽  
Matrix Fraction ◽  
De Novo Protein Synthesis

The principal alpha-tubulin within Chlamydomonas reinhardtii flagellar axonemes differs from the major alpha-tubulin in the cell body. We show that these two isoelectric variants of alpha-tubulin are related to one another since posttranslational modification of the cell body precursor form converts it to the axonemal form. During flagellar assembly, precursor alpha-tubulin enters the flagella and is posttranslationally modified within the flagellar matrix fraction prior to or at the time of its addition to the growing axonemal microtubules. Experiments designed to identify the nature of this posttranslational modification have also been conducted. When flagella are induced to assemble in the absence of de novo protein synthesis, tritiated acetate can be used to posttranslationally label alpha-tubulin in vivo and, under these conditions, no other flagellar polypeptides exhibit detectable labeling.

scholarly journals Viral Gene Expression Patterns in Human Herpesvirus 6B-Infected T Cells

2002 ◽  
Vol 76 (15) ◽  
pp. 7578-7586 ◽  
Author(s):  
Bodil Øster ◽  
Per Höllsberg
Keyword(s):  
Gene Expression ◽  
T Cells ◽  
Protein Synthesis ◽  
De Novo ◽  
Expression Patterns ◽  
Human Herpesvirus ◽  
Viral Gene Expression ◽  
Polymerase Activity ◽  
Viral Gene ◽  
De Novo Protein Synthesis

ABSTRACT Herpesvirus gene expression is divided into immediate-early (IE) or α genes, early (E) or β genes, and late (L) or γ genes on the basis of temporal expression and dependency on other gene products. By using real-time PCR, we have investigated the expression of 35 human herpesvirus 6B (HHV-6B) genes in T cells infected by strain PL-1. Kinetic analysis and dependency on de novo protein synthesis and viral DNA polymerase activity suggest that the HHV-6B genes segregate into six separate kinetic groups. The genes expressed early (groups I and II) and late (groups V and VI) corresponded well with IE and L genes, whereas the intermediate groups III and IV contained E and L genes. Although HHV-6B has characteristics similar to those of other roseoloviruses in its overall gene regulation, we detected three B-variant-specific IE genes. Moreover, genes that were independent of de novo protein synthesis clustered in an area of the viral genome that has the lowest identity to the HHV-6A variant. The organization of IE genes in an area of the genome that differs from that of HHV-6A underscores the distinct differences between HHV-6B and HHV-6A and may provide a basis for further molecular and immunological analyses to elucidate their different biological behaviors.

De novo protein synthesis in relation to ammonia and proline accumulation in water stressed white clover

2004 ◽  
Vol 31 (8) ◽  
pp. 847 ◽  
Author(s):  
Tae-Hwan Kim ◽  
Bok-Rye Lee ◽  
Woo-Jin Jung ◽  
Kil-Yong Kim ◽  
Jean-Christophe Avice ◽  
...  
Keyword(s):  
Protein Synthesis ◽  
Water Deficit ◽  
White Clover ◽  
De Novo ◽  
Proline Accumulation ◽  
Leaf Water ◽  
Total N ◽  
Water Parameters ◽  
Leaves And Roots ◽  
De Novo Protein Synthesis

The kinetics of protein incorporation from newly-absorbed nitrogen (N, de novo protein synthesis) was estimated by 15N tracing in 18-week-old white clover plants (Trifolium repens L. cv. Regal) during 7 d of water-deficit treatment. The physiological relationship between kinetics and accumulation of proline and ammonia in response to the change in leaf-water parameters was also assessed. All leaf-water parameters measured decreased gradually under water deficit. Leaf and root dry mass was not significantly affected during the first 3 d when decreases in leaf-water parameters were substantial. However, metabolic parameters such as total N, proline and ammonia were significantly affected within 1 d of commencement of water-deficit treatment. Water-deficit treatment significantly increased the proline and NH3–NH4+ concentrations in both leaves and roots. There was a marked reduction in the amount of N incorporated into the protein fraction from the newly absorbed N (NANP) in water-deficit stressed plants, particularly in leaf tissue. This reduction in NANP was strongly associated with an increased concentration of NH3–NH4+ in roots (P≤0.05) and proline (P≤0.01) in leaves and roots. These results suggest that proline accumulation may be a sensitive biochemical indicator of plant water status and of the dynamics of de novo protein synthesis in response to stress severity.

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