Subunit structure and function of Micrococcus cryophilus glutamyl transfer RNA synthetase

Biochemical and Genetic Characterization of a Temperature-Sensitive, Tryptophanyl-Transfer Ribonucleic Acid Synthetase Mutant of Bacillus subtilis

“…For example, in a system in which subunit assembly has been shown to be a temperature-dependent process, only the dimerized form of wild-type E. coli prolyl-tRNA synthetase is active (22). The thermolability of wild-type glutamyl-tRNA synthetase of the obligate psychrophile Micrococcus cryophilus has also been attributed to a dissociation into inactive subunits (26). A mutant of this organism, capable of growth at higher temperatures normally restrictive for the wild type, has a glutamyl-tRNA synthetase whose activity and subunit structure are stable (26).…”

“…First, the genus Bacillus has the genetic capacity to form bacterial endospores, and in this respect it provides the added attraction of a developmental system. This is in marked contrast to those bacterial genera so far studied for which activating enzyme mutants are known, namely Escherichia (12, 14, 37), Salmonella (32), and Micrococcus (26). Second, the structural genes coding for those enzymes involved in the synthesis of L-tryptophan are known to be cotransferred by a single piece of transforming deoxyribonucleic acid (DNA) and represent a genetic regulatory unit (2,18).…”

Psychrophilic bacteria.

“…However, as they point out, this does not account for the decline in the growth of the organism between the optimum and maximum growth temperatures. When a cell-free extract prepared from the psychrotrophic bacterium Micrococcus cryophilus was subjected to 5 C above the maximal growth temperature for the organism, three aminoacyl-tRNA synthetases (glutamic acid, histidine, and proline) were found to be temperature sensitive (109,110,111,112). Unfortunately, the experiments were not carried out 1 or 2 C above the maximal growth temperature for M. cryophilus.…”

Defects of Two Temperature-Sensitive Lysyl-Transfer Ribonucleic Acid Synthetase Mutants of Bacillus subtilis

“…However, aggregation to a 150,000 molecular weight form could have occurred during the assay. Aminoacyl-tRNA synthetase activity has been correlated with quaternary structure for mutants of the alanyl-(3, 15), lysyl-(8), and phenylalanyl-tRNA synthetases (2) of E. coli, and the glutamyl-tRNA synthetase of Micrococcus cryophilus (22). An alanyl-tRNA synthetase mutant (15) lacks attachment activity and is apparently defective in subunit association.…”

“…Temperature-sensitive mutants of aminoacyl-transfer ribonucleic acid (tRNA) synthetases have been used to demonstrate the roles of these enzymes in protein synthesis (18,25) and to implicate them in the regulation of amino acid biosynthesis (25). In addition to providing a means for studying their physiological roles, aminoacyl-tRNA synthetase mutants have also been used to correlate activity with the subunit structure of the enzyme (2,3,8,15,22). As part of a study of the roles of these enzymes in the developmental cycle of Bacillus subtilis, we have attempted to isolate and characterize temperature-sensitive mutants of the lysyl-tRNA synthetase (LRS) of this organism.…”