SPECIFICITY AND TIME OF THE APPEARANCE OF HIS(-TYPHIMURIUM() REVERSIONS INDUCED BY HISTIDINE STARVATION IN SALMONELLA)

It was previously established that reversion of the hisG46 allele of S almonella typhimurium to prototrophy occurred upon histidine starvatio n. In this paper, it was shown that histidine starvation does not affe ct the appearance of mutants resistant to L-arabinose and rifampicin. Threonine starvation did not change the frequency of His(+) revertants . Analysis of His(+) revertant clones did not reveal additional L-arab inose resistance mutations. Thus, these experiments allowed the conclu sion that amino acid starvation does not lead to a nonspecific increas e in the mutation rate. In addition, it was shown that spontaneous His (+) revertants start to arise after two to three hours of histidine st arvation, this process lasting for four days. Nevertheless, original H is(+) cells did not grow in a culture generating His(+) revertants. Tr aces of histidine and novobiocin added to a minimal medium retarded re version realization. However, the occurrence of revertants was not mar kedly inhibited by chloramphenicol. Based on the results, it is assume d that adaptive His(+) reversions occurred due to a special mode of re plication induced upon histidine starvation and requiring no de novo p rotein synthesis.