Regulation of the Serratia marcescensExtracellular Nuclease: Positive Control by a Homolog of P2 Ogr Encoded by a Cryptic Prophage

Abstract

The Serratia marcescensextracelluar nuclease is a secreted protein that is subject to growth phase and SOS control. Regulatory mutants affecting nuclease expression have been isolated that define a new locus, nucC, essential for transcription of the nuclease gene nucA. The cloned nucCgene is able to activate efficient expression from the nucApromoter in Escherichia coli, where it normally is poorly expressed. NucC is very similar to the bacteriophage P2 Ogr protein, a transcriptional activator essential for P2 late gene expression. NucC is able to replace P2 Ogr to support the growth of P2 ogr −mutants in E. coli.Ogr is a poor activator of the nuclease promoter in E. coli, but the related δ gene product from satellite phage P4 is highly effective. The presence of genes encoding a lysozyme and a putative porin or holin in the nucCoperon suggests that nucCmay be part of a cryptic prophage genome. The putative holin-like membrane protein is required in E. colifor extracellular secretion of the S. marcescensnuclease.