INDUCTION OF THE SOS-RESPONSE IN TEST BACTERIA BY BACILLUS-INTERMEDIUS RNASE

This paper deals with the induction of the SOS-functions of a bacteria l cell by the exogenous ribonuclease of Bacillus intermedius. Two test systems were employed, which made it possible to quantitatively estim ate SOS-response induction activity in gram positive and gram-negative bacteria. It was established that the catalytically active enzyme eli cits the SOS-response in the cells of Escherichia coli PQ 37 and cause s prophage induction in the lysogenic strain Bacillus subtilis 168 phi 105 WT (a phenomenon related to the SOS-response). An enzyme with a H is(101)Glu-substituted active center, exhibiting residual catalytic ac tivity, failed to induce the SOS-response in an SOS-chromotest with E. coil PQ 37, indicating dependence of the SOS-inducing effect of the e nzyme on its catalytic activity. It is suggested that the effect of ac tive ribonuclease on membrane-bound and cytoplasmic RNA causes a chang e in the nucleotide pool and, consequently, elicits the SOS-response o f the cell.