REGULATION OF THE SERRATIA-MARCESCENS EXTRACELLULAR NUCLEASE - POSITIVE CONTROL BY A HOMOLOG OF P2 OGR ENCODED BY A CRYPTIC PROPHAGE

The Serratia marcescens extracelluar nuclease is a secreted protein th at is subject to growth phase and SOS control. Regulatory mutants affe cting nuclease expression have been isolated that define a new locus, nucC, essential for transcription of the nuclease gene nucA. The clone d nucC gene is able to activate efficient expression from the nucA pro moter in Escherichia coli, where it normally is poorly expressed. NucC is very similar to the bacteriophage P2 Ogr protein, a transcriptiona l activator essential for P2 late gene expression. NucC is able to rep lace P2 Ogr to support the growth of P2 ogr(-) mutants in E. coil. Ogr is a poor activator of the nuclease promoter in E. coli, but the rela ted delta gene product from satellite phage P4 is highly effective. Th e presence of genes encoding a lysozyme and a putative porin or holin in the nucC operon suggests that nucC may be part of a cryptic prophag e genome. The putative holin-like membrane protein is required in E. c oli for extracellular secretion of the S. marcescens nuclease. (C) 199 6 Academic Press Limited