Influence of Modified tRNATyr on the Activation of Tyrosine Catalyzed by Tyrosyl-tRNA Synthetase from Saccharomyces cerevisiae

Yeast tyrosyl-tRNA synthetase (TyrRS, EC 6.1.1.1) is a homodimeric enzyme capable of binding only one molecule of its macromolecular substrate, tRNATyr. The reactive intermediate tyrosyl adenylate is formed from tyrosine and ATP in the first reaction step, which can be conveniently assayed by pyrophosphate exchange. In order to determine the number of active sites per homodimer, the kinetics of pyrophosphate exchange was measured in the presence of the tRNATyr analogue unable to accept the amino acid. The analogue was found to form the expected equimolar complex with dimeric enzyme. It was a competitive inhibitor of pyrophosphate exchange with respect to ATP and non-competitive with respect to tyrosine. Inhibition cannot exceed 50%, suggesting the simplest model in which yeast TyrRS is a symmetrical dimer, possessing two identical active sites, both capable of catalyzing the formation of tyrosyl adenylate

Functional Inactivation and Appearance of Breaks in RNA Chains Caused by Gamma Irradiation of Escherichia coli Ribosomes

70S ribosomes and 30S ribosomal subunits from Escherichia coli MRE 600 were exposed to gamma irradiation at -80szC. Exponential decline of activity with dose was observed when the ability of ribosomes to support the synthesis of polyphenylalanine was assayed. Irradiated ribosomes showed also an increased thermal lability. D(37) values of 2.2 MR and 4.8 MR, corresponding to radiation-sensitive molecular weights of 3.1 × 10(5) and 1.4 × 10(5), were determined for inactivation of 70S ribosomes and 30S subunits, respectively. Zone sedimentation analysis of RNA isolated from irradiated bacteria or 30S ribosomal subunits showed that at average, one chain scission occurs per four hits into ribosomal RNA. From these results it was concluded that the integrity of only a part of ribosomal proteins (the sum of their molecular weights not exceeding 1.4 × 10(5)) could be essential for the function of the 30S subunit in the polymerization of phenylalanine. This amount is smaller if the breaks in the RNA chain inactivate the ribosome

A high-coverage Neandertal genome from Vindija Cave in Croatia

To date, the only Neandertal genome that has been sequenced to high quality is from an individual found in Southern Siberia. We sequenced the genome of a female Neandertal from ~50,000 years ago from Vindija Cave, Croatia, to ~30-fold genomic coverage. She carried 1.6 differences per 10,000 base pairs between the two copies of her genome, fewer than present-day humans, suggesting that Neandertal populations were of small size. Our analyses indicate that she was more closely related to the Neandertals that mixed with the ancestors of present-day humans living outside of sub-Saharan Africa than the previously sequenced Neandertal from Siberia, allowing 10 to 20% more Neandertal DNA to be identified in present-day humans, including variants involved in low-density lipoprotein cholesterol concentrations, schizophrenia, and other diseases

A high-coverage Neandertal genome from Vindija Cave in Croatia

To date, the only Neandertal genome that has been sequenced to high quality is from an individual found in Southern Siberia. We sequenced the genome of a female Neandertal from ~50,000 years ago from Vindija Cave, Croatia, to ~30-fold genomic coverage. She carried 1.6 differences per 10,000 base pairs between the two copies of her genome, fewer than present-day humans, suggesting that Neandertal populations were of small size. Our analyses indicate that she was more closely related to the Neandertals that mixed with the ancestors of present-day humans living outside of sub-Saharan Africa than the previously sequenced Neandertal from Siberia, allowing 10 to 20% more Neandertal DNA to be identified in present-day humans, including variants involved in low-density lipoprotein cholesterol concentrations, schizophrenia, and other diseases