TRANSCRIPTIONAL ORGANIZATION AND REGULATION OF EXPRESSION OF REGION-1OF THE ESCHERICHIA-COLI K5 CAPSULE GENE-CLUSTER

The transcriptional organization and regulation of region 1 expression of the Escherichia coil K5 capsule gene cluster were studied, Region 1 was transcribed as an 8.0-kb polycistronic mRNA which Has processed to form a separate 13-kb transcript encoding the 3'-most gene kpsS. Tr anscription of region I of the E. coil K5 capsule gene cluster was dir ected from a single promoter 225 bp upstream of a previously unidentif ied gene, kpsF, The promoter had -35 and -10 consensus sequences typic al of an E. coli sigma 70 promoter, with no similarities to binding si tes for other sigma factors, Two integration host factor (IHF) binding site consensus sequences were identified 110 bp upstream and 130 bp d ownstream of the transcription start site. In addition, two AT-rich re gions separated by 16 bp identified upstream of the region I promoter were conserved upstream of the region 3 promoter, The kpsF gene was 98 .8% identical with the kpsF gene identified in the E. coli K1 antigen gene cluster and confirms that the kpsF gene is conserved among group II capsule gene clusters, An intragenic Rho-dependent transcriptional terminator was discovered within the kpsF gene, No essential role for KpsF in the expression of the K5 antigen could he established. The tem perature regulation of region 1 expression was at the level of transcr iption, with no transcription detectable in cells grown at 18 degrees C, Mutations in regulatory genes known to control temperature-dependen t expression of a number of virulence genes had no effect on the tempe rature regulation of region 1 expression. Likewise, RfaH, which is kno wn to regulate expression of E. coli group II capsules had no effect o n the expression of region 1. Mutations in the himA and himD genes whi ch encode the subunits of the IHF led to a fivefold reduction in the e xpression of KpsE at 37 degrees C, confirming a regulatory role for IH F in the expression of region 1 genes.