Biomedical subjects

M Jasin

Publications and source records attributed to M Jasin.

59 records · Page 4Linked to original sources

PubMed1984

Dispensable pieces of an aminoacyl tRNA synthetase which activate the catalytic site.

Recent data suggest that size polymorphism of aminoacyl tRNA synthetase is due to variable fusions of additional functional domains to a catalytic core so that, in a large synthetase, a substantial part of the polypeptide is dispensable for catalytic activity. We demonstrate here that a dispensable domain, joined to the catalytic core of a large synthetase, can activate the catalytic sites. This is shown by complementation of an activity-deficient mutant enzyme by protein fragments that contain internal deletions within the catalytic domain and are themselves devoid of activity. The complementation is dependent upon the presence of a defined segment of polypeptide that is remote in the sequence from the catalytic core. Substantial coupling has been established between dispensable and indispensable component pieces. This could be a mechanism to build efficiently large enzymes which integrate the catalytic sites with other previously shown functional roles.

Alanine-tRNA Ligase↗

PubMed1984

Deletion of an essential gene in Escherichia coli by site-specific recombination with linear DNA fragments.

Deletion of an essential gene in Escherichia coli was accomplished by transformation of linear DNA fragments that have a Kanr gene segment flanked by sequences homologous to closely spaced regions on the E. coli chromosome. Selection for a double crossover within homologous sequences can effectively delete an entire gene. Cell viability is maintained by provision of the essential gene on a plasmid with a temperature-sensitive replicon, resulting in cells which have a temperature-sensitive phenotype.

Base Sequence↗

PubMed1984

Size polymorphism and the structure of aminoacyl-tRNA synthetases.

Although aminoacyl-tRNA synthetases catalyze the same chemical reaction, the individual enzymes have a wide range of sizes. Proteolytic digestion has yielded active catalytic fragments of two synthetases. A set of gene deletions in a large synthetase has been used successfully in the creation of a variety of enzyme fragments that have been studied individually; a fragment with about half of the total polypeptide is sufficient to aminoacylate tRNA in vivo. The results suggest that size polymorphism is caused by fusion, to a core catalytic segment, of variable amounts of additional polypeptide sequences. These sequences may serve to impart additional functions. For example, in one case, a synthetase binds to its own gene promoter and regulates transcription.

Amino Acyl-tRNA Synthetases↗

PubMed1983

Cycloheximide resistance in yeast: the gene and its protein.

Mutations in the yeast gene CYH2 can lead to resistance to cycloheximide, an inhibitor of eukaryotic protein synthesis. The gene product of CYH2 is ribosomal protein L29, a component of the 60S ribosomal subunit. We have cloned the wild-type and resistance alleles of CYH2 and determined their nucleotide sequence. Transcription of CYH2 appears to initiate and terminate at multiple sites, as judged by S1 nuclease analysis. The gene is transcribed into an RNA molecule of about 1082 nucleotides, containing an intervening sequence of 510 nucleotides. The splice junction of the intron resides within a codon near the 5' end of the gene. In confirmation of peptide analysis by Stocklein et al. (1) we find that resistance to cycloheximide is due to a transversion mutation resulting in the replacement of a glutamine by glutamic acid in position 37 of L29.

Alleles↗

PubMedDate not supplied

Modular arrangement of functional domains along the sequence of an aminoacyl tRNA synthetase.

Gene deletions show that much of Escherichia coli alanine tRNA synthetase is dispensable for each of three activities and that these activities appear to require specific domains arranged linearly along the polypeptide. Thus, variable fusions of extra polypeptide domains to a catalytic core may account for the diverse of aminoacyl tRNA synthetases.

Adenosine Triphosphate↗