Nuclease: Positive Control by a Homolog of P2 Ogr Encoded by a Cryptic Prophage

The Serratia marcescens extracelluar nuclease is a secreted protein that is1Department of Biochemical and Biophysical Sciences subject to growth phase and SOS control. Regulatory mutants affecting nuclease expression have been isolated that define a new locus, nucC,University of Houston essential for transcription of the nuclease gene nucA. The cloned nucC geneHouston, Texas 77204-5934 USA is able to activate efficient expression from the nucA promoter in Escherichia coli, where it normally is poorly expressed. NucC is very similar to the2Department of Microbiology bacteriophage P2 Ogr protein, a transcriptional activator essential for P2 and Immunology, Medical late gene expression. NucC is able to replace P2 Ogr to support the growth College of Virginia, Virginia of P2 ogr − mutants in E. coli. Ogr is a poor activator of the nuclease promoter Commonwealth University in E. coli, but the related d gene product from satellite phage P4 is highly Richmond, Virginia effective. The presence of genes encoding a lysozyme and a putative porin 23298-0678, USA or holin in the nucC operon suggests that nucC may be part of a cryptic prophage genome. The putative holin-like membrane protein is required in E. coli for extracellular secretion of the S. marcescens nuclease