Regulatory mutants and transcriptional control of the Serratia marcescens extracellular nuclease gene

Abstract
Summary: The extracellular nuclease of Serratia marcescens is regulated in a complex fashion. Unlike most catabolic enzymes, it appears not to be substrate regulated. However we have shown it to be regulated by an SOS‐like system in S. marcescens. Additionally nuclease expression is regulated In a growth‐phase‐dependent manner. In this work we demonstrate that growth‐phase‐dependent regulation is at the transcriptional level. The putative LexA‐binding site which mediates SOS regulation is shown to act as an operator site in viva. The boundaries of a minimal promoter, stilt regulated by growth phase and SOS regulation, are defined along with the transcriptional start site. However, a region upstream of the nuclease promoter is shown to enhance significantly the expression of nuclease.