MUTATION IN THE STRUCTURAL GENE FOR RELEASE FACTOR-1 (RF-1) OF SALMONELLA-TYPHIMURIUM INHIBITS CELL-DIVISION

A temperature-sensitive mutant of Salmonella typhimurium LT2 was isola ted. At the nonpermissive temperature cell division stopped and multin ucleated filaments were formed. DNA, RNA, or protein synthesis was not affected until after about two generations, Different physiological c onditions, such as anaerobiosis and different growth media, suppress t he division deficiency at high temperatures. Certain mutations causing a reduced polypeptide chain elongation rate also suppress the divisio n deficiency. The mutation is recessive and shown to be in the structu ral gene for release factor 1 (prfA). DNA sequencing of both the wild- type (prfA(+)) and mutant (prfA101) allele revealed a GC-to-AT transit ion in codon 168. Like other known prfA mutants, prfA101 can suppress amber mutations. The division defect in the prfA101 mutant strain coul d not be suppressed by overexpression of the ftsQAZ operon. Moreover, at the nonpermissive temperature the mutant shows a normal heat shock and SOS response and has a normal ppGpp level. We conclude that the pr fA101-mediated defect in cell division is not directed through any of these metabolic pathways, which are all known to affect cell division. We speculate that the altered release factor 1 induces aberrant synth esis of an unidentified protein(s) involved in the elaborate process o f septation.