Mutagenesis of the P2 promoter of the major outer membrane protein gene of Chlamydia trachomatis

Abstract

On the basis of position from the transcription start site, the P2 promoter of the gene encoding the major outer membrane protein (ompA) of Chlamydia trachomatis consists of a -35 hexamer region of -42 aaaaaga TATACAaa -28 and an unusual, GC-rich -10 hexamer region of -13 tTATCGCt -6. The P2 promoter was analyzed by in vitro transcription of templates containing deletions and site-specific mutations. The 5' extent of P2 was located at bp -42. Replacement of wild-type sequence with two G's at positions -41 and 40, -35 and 34, and -29 and 28 resulted in severely decreased transcription. Additionally, the spacing between the -35 and -10 hexamers could not be shortened without adversely affecting in vitro activity. Substitution of G at position -13, -10, -7, or -6 had little or no effect on transcription, whereas substitution of G at -11 or -12 significantly decreased promoter strength. Triple point mutations which changed the -10 hexamer from TATCGC to TATTAT,TATATT, or TATAAT had little effect on promoter activity. Unlike the partially purified C. trachomatis sigma66-RNA polymerase used in this study, purified Escherichia coli sigma70-RNA polymerase did not recognize the wild-type P2 promoter. Mutant P2 templates with -10 hexamers that resembled the consensus recognition site were transcribed by E. coli holoenzyme in vitro, suggesting that C. trachomatis sigma66-RNA polymerase has special promoter recognition properties not found in E. coli sigma70-holoenzyme.