Conserved strategies of RNA polymerase I hibernation and activation

RNA polymerase (Pol) I transcribes the ribosomal RNA precursor in all eukaryotes. The mechanisms ‘activation by cleft contraction’ and ‘hibernation by dimerization’ are unique to the regulation of this enzyme, but structure-function analysis is limited to baker’s yeast. To understand whether regulation by such strategies is specific to this model organism or conserved among species, we solve three cryo-EM structures of Pol I from Schizosaccharomyces pombe in different functional states. Comparative analysis of structural models derived from high-resolution reconstructions shows that activation is accomplished by a conserved contraction of the active center cleft. In contrast to current beliefs, we find that dimerization of the S. pombe polymerase is also possible. This dimerization is achieved independent of the ‘connector’ domain but relies on two previously undescribed interfaces. Our analyses highlight the divergent nature of Pol I transcription systems from their counterparts and suggest conservation of regulatory mechanisms among organisms.

Possible functions of the conserved peptide encoded by the RNA-precursor of miR-156a in plants of the family Brassicaceae

Recent studies have shown that the primary transcripts of some microRNA genes (pri-miRNAs) are able to express short proteins (peptides) ranging usually from 12-15 amino acid residues to around 30 residues in length. These peptides, called miPEPs, may participate in the regulation of transcription of their own pri-miRNAs. Using bioinformatic comparative analysis of pri-miRNA sequences in plant genomes, we previously discovered a new group of miPEPs (miPEP-156a), which is encoded by pri-miR156a in several dozen species from the Brassicaceae family. Exogenous peptides miPEP-156a can effectively penetrate plant seedlings through the root system and spread systemically to the leaves of young seedlings. At the same time, a moderate morphological effect is observed, which consists in accelerated growth of the main root of the seedling. In parallel, a positive effect is observed at the level of pri-miR156a expression. It is important that the effects at the morphological and molecular levels are seemingly related to the ability of the peptide to quickly transfer into the cell nuclei and bind to nuclear chromatin. In this work, the secondary structure of the peptide was also experimentally established, and changes in this structure in the complex with DNA were shown.

Role of sulfur in proton-induced collisions of RNA prebiotic precursors

Charge transfer theoretical treatment of proton-induced collisions on the sulfur-containing cyclic RNA precursor, 2-aminothiazole. Role of sulfur in the process and implications in prebiotic selective synthesis.

Effect of short- and long-lasting chilling on pre-rRNA synthesis and transport in root meristematic cells of three soybean cultivars

<p>Autoradiographic studies of ³H-uridine incorporation (20-min incubation) and dynamics of radioactive particle translocation from nucleolus into cytoplasm (following 80-min postincubation in non-radioactive medium) in root meristematic cells of soybean have been carried out. The experiment was performed with plants subjected to 4-day acclimation in chilling or subjected to 2-hour cold stress and control plants. Three cultivars of soybean: Mazowia, Polan and Progres (cultivated in Poland) were used in the experiment.</p><p>It has been shown that in control conditions the greatest number of RNA precursor is incorporated into nucleoli after 20-min incubation. Following 80-min postincubation cytoplasm is the most radioactive area of the cell - this mainly testifies to dynamic translocation of radioactive ribosome subunits from nucleolus into cytoplasm.</p><p>In chilling conditions the reduction of ³H-uridine incorporation into cells occurs, as compared to control conditions. Plants subjected to a 4-day acclimation incorporate the radioactive precursor more intensively than plants subjected to cold stress.</p><p>Following 80-min postincubation - in the case of acclimated plants - the nucleolus is the most radioactive area of the cell, which testifies to accumulation of pre-rRNA in it. After the cold stress cytoplasm is more radioactive than the nucleolus. In all three cultivars the processes of synthesis and transport of pre-rRNA particles are similar, only their intensity is different.</p><p>Morphometric measurements of nucleoli in all cultivars subjected to 4-day chilling have shown that root cell nucleoli are larger than those in control. This phenomenon can be connected with stronger inhibition of rRNA transport than its synthesis.</p>

Differential stability of mitochondrial mRNA in HeLa cells.

The physiological significance and metabolism of oligoadenylated and polyadenylated human mitochondrial mRNAs are not known to date. After study of eight mitochondrial transcripts (ND1, ND2, ND3, ND5, CO1, CO2, ATP6/8 and Cyt. b) we found a direct correlation between the half-lives of mitochondrial mRNAs and their steady-state levels. Investigation of the mt-mRNA decay after thiamphenicol treatment indicated that three transcripts (ND2, ND3 and Cyt. b) are significantly stabilized after inhibition of mitochondrial translation. Careful analysis one of them, ND3, showed that inaccurate processing of the H-strand RNA precursor may occasionally occur between the ND3 and tRNA(Arg) locus leading to synthesis of ND3 mRNAs lacking the STOP codon. However, analysis of the oligo(A) fraction observed in case of the ND3 indicates that partially polyadenylated mRNAs are linked rather to the transcription process than to the translation-dependent deadenylation. Analysis of ND3 mRNA turnover in cells with siRNA-mediated knock-down of the mitochondrial poly(A) polymerase shows that strongly decreased polyadenylation does not markedly affect the decay of this transcript. We present a model where oligoadenylated mitochondrial transcripts are precursors of molecules containing full length poly(A) tails.