Two mRNA analogs, pUUCUAAA (with stop codon UAA) and pUUCUCAA (with Ser codon UCA) containing a perfluoroarylazido group at U4, were used to study the position relative to the 18S rRNA for the first nucleotide of the codon located in the A site of the human 80S ribosome. To place UAA or UCA in the A site, UCC-recognizing tRNAPhe was bound in the P site. With each analog, crosslinking was detected for highly conserved fragment 1816-1831, which contains invariant dinucleotide A1823/A1824 and is in helix 44 at the 3' end of the 18S rRNA. Since 18S rRNA modification did not depend on whether the U4 photoreactive group was in the sense or stop codon, it was assumed that polypeptide chain release factor 1 directly recognizes the trinucleotide of a stop codon located in the A site.

Base Sequence↗

PubMedDate not supplied

[Influence of individual domains of the translation termination factor eRF1 on induction of the GTPase activity of the translation termination factor eRF3].

Translation termination in eukaryotes is governed by two proteins, belonging to the class-1 (eRF1) and class-2 (eRF3) polypeptide release factors. eRF3 catalyzes hydrolysis of GTP to GDP and inorganic phosphate in the ribosome in the absence of mRNA, tRNA, aminoacyl-tRNA and peptidyl-tRNA but needs the presence of eRF1. It's known that eRF1 and eRF3 interact with each other in vitro and in vivo via their C-terminal regions. eRF1 consists of three domains - N, M, and C. In this study we examined the influence of individual domains of the human eRF1 on induction of the human eRF3 GTPase activity in the ribosome in vitro. It was shown that none of the N-, M-, C- and NM-domains induces eRF3 GTPase activity in presence of the ribosomes. MC-domain does induce GTPase activity of eRF3 but four times less efficient than full-length eRF1, therefore, MC-domain (and very likely M-domain) binds to the ribosome in the presence of eRF3. Based on these data and taking into account the data available in literature, a conclusion was drawn that the N domain of eRF1 is not essential for eRF1-dependent induction of the eRF3 GTPase activity. A working hypothesis is formulated, postulating that GTPase activity eRF3 during the translation termination is associated with the intermolecular interactions of GTP/GDP, GTPase center of the large ribosomal subunit (60S), MC-domain of eRF1, C-terminal region and GTP-binding domains of eRF3, but without participation of the N-terminal region of eRF3.

Animals↗

PubMedDate not supplied

[The tRNA anticodon is recognized by aminoacyl-tRNA-synthetase].

Data concerning the regions of tRNA molecules recognized by cognate aminoacyl-tRNA synthetases and obtained recently by the new methods (the synthesis of mutant tRNA genes and their transcription in vitro, chimeric suppressor tRNA, RNA engineering) are briefly discussed. The results of several laboratories are in full agreement with the hypothesis proposed earlier on the role of a tRNA anticodon as a specific region by which the enzyme identifies various tRNAs. More than half of tRNAs belong to the group recognized by the aminoacyl-tRNA synthetases by this mechanism. The behavior of natural and artificially constructed tRNAs which contain modified anticodons, but conserve amino acid specificity in the reaction of aminoacylation, indicates that in some tRNAs the role of the anticodon in the tRNA identity is minor if any. This group of tRNA is recognized by the aminoacyl-tRNA synthetases predominantly via the double helical region of the molecule. The authors discuss the significance of the absence of topographic conservatism in the mechanism by which tRNAs are recognized by the aminoacyl-tRNA synthetases.

Amino Acyl-tRNA Synthetases↗

PubMedDate not supplied

[Hydrodynamic properties and optic anisotrophy of the molecules of transfer RNA in aqueous solutions].

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Chemical Phenomena↗

PubMedDate not supplied

[Nuclear precursors for ceruloplasmin-coding messenger RNA from rat liver].

The distribution of the sequences coding for ceruloplasmin (CP) in rat liver heterogeneous nuclear RNA (hnRNA) was studied using highly specific CP cDNA as a hybridization probe. The content of CP-coding sequences in poly(A)-containing and poly(A)-free subfractions of hnRNA was shown to be respectively 1 and 27 equivalents of CP mRNA molecule per one hepatocyte. The gel electrophoresis of hnRNA under strongly denaturing conditions with the subsequent transfer of RNA to diazobenzyloxymethyl paper and hybridization with [32P]-cDNA probe showed that CP mRNA sequences were of multiple molecular weight distribution. In particular, 9.0, 6.6, 2.4 and 1.6 megadalton fractions of non-polyadenylate hnRNA carried CP-coding sequences while the only hand that hybridized to CP cDNA was detected in polyadenylated hnRNA. This band was of a molecular weight 1.1-1.2 megadaltons corresponding to that of cytoplasmic CP mRNA. The hybridization of high molecular weight hnRNA with full-length CP cDNA followed by the determination of the size of cDNA fragments protected against SI nuclease demonstrated that coding sequences of CP pre-mRNA are interrupted by intervening sequences.

Animals↗

PubMedDate not supplied

[Reverse transcription of influenza virion RNA without exogenous primer].

Reverse transcriptase has been shown to transcribe virion DNA of influenza A virus without an exogeneous primer. At least six virion RNA segments are transcribed with the formation of complementary 4S DNA product. A possible primer function of hairpin structures at the 3'-end of virion RNA segments is discussed.

DNA↗