DIFFERENTIAL EXPRESSION OF GENES IN THE VIR REGULON OF STREPTOCOCCUS-PYOGENES IS CONTROLLED BY TRANSCRIPTION TERMINATION

Streptococcal C5a peptidase (SCP), encoded by scpA in Streptococcus py ogenes, is a surface molecule which is able to cleave and inactivate t he chemotactic factor C5a. The scpA gene is part of the vir regulon an d subject to positive regulation by the Mga protein. It is down-regula ted compared to another Mga-activated gene, emm. A chloramphenicol ace tyltransferase (CAT) reporter gene was used to measure scpA promoter a ctivity. Previous work had shown that when a large portion of the scpA promoter region was deleted, expression of CAT increased relative to the wild-type. This deleted region was found to contain an inverted re peat. In this study we show that the inverted repeat in the leader mRN A is the site of transcription termination, which down-regulates expre ssion of scpA. This is a novel mechanism for regulation of gene expres sion in S. pyogenes. A specific deletion of the inverted repeat in the scpA promoter-CAT reporter construct was made using inverse PCR. Expr ession was measured from single-copy chromosomal integrants. When the inverted repeat was deleted, expression increased. Furthermore, Northe rn hybridization confirmed the existence of a truncated transcript, co nsistent with a transcription termination mechanism.