TRANSCRIPTIONAL REGULATION OF THE STREPTOCOCCUS-SALIVARIUS 57.I UREASE OPERON

The Streptococcus salivarius 57.I are cluster was organized as an oper on, beginning with ureI, followed by ureABC (structural genes) and ure EFGD (accessory genes). Northern analyses revealed transcripts encompa ssing structural genes and transcripts containing the entire operon. A sigma(70)-like promoter could be mapped 5' to ureI (PureI) by primer extension analysis. The intensity of the signal increased when cells w ere grown at an acidic pH and was further enhanced by excess carbohydr ate. To determine the function(s) of two inverted repeats located 5' t o PureI, transcriptional fusions of the full-length promoter region (P ureI), or a deletion derivative (PureI Delta 100), and a promoterless chloramphenicol acetyltransferase (CAT) gene were constructed and inte grated into the chromosome to generate strains PureICAT and PureI Delt a 100CAT, respectively. CAT specific activities of PureICAT were repre ssed at pH 7.0 and induced at pH 5.5 and by excess carbohydrate. In Pu reI Delta 100CAT, CAT activity was 60-fold higher than in PureICAT at pH 7.0 and pH induction was nearly eliminated, indicating that express ion was negatively regulated. Thus, it was concluded that PureI was th e predominant, regulated promoter and that regulation was governed by a mechanism differing markedly from other known mechanisms for bacteri al urease expression.