[Induction of the SOS-response with Bacillus intermedius RNAase]

This paper deals with the induction of the SOS-functions of a bacterial cell by the exogenous ribonuclease of Bacillus intermedius. Two test systems were employed, which made it possible to quantitatively estimate SOS-response induction activity in gram-positive and gram-negative bacteria. It was established that the catalytically active enzyme elicits the SOS-response in the cells of Escherichia coli PQ 37 and causes prophage induction in the lysogenic strain Bacillus subtilis 168 phi 105 WT (a phenomenon related to the SOS-response). An enzyme with a His101Glu-substituted active center, exhibiting residual catalytic activity, failed to induce the SOS-response in an SOS-chromotest with E. coli PQ 37, indicating dependence of the SOS-inducing effect of the enzyme on its catalytic activity. It is suggested that the effect of active ribonuclease on membrane-bound and cytoplasmic RNA causes a change in the nucleotide pool and, as a consequence, elicits the SOS-response of the cell.