The expression and transcriptional organisation of region 1 of the Escherichia coli K5 capsule gene cluster.
2015-11-19T09:10:46Z (GMT) by
E. coli strains associated with extra-intestinal infections are generally encapsulated. The gene clusters required for expression of group II capsules comprise three functional regions. The expression of region 1, which is conserved between the different serotypes was investigated. The K5 kps region 1 was transcribed as an 8.0 kb polycistronic mRNA which was processed to form a 1.3 kb transcript encoding the most promoter-distal gene kpsS. Transcription initiated at a single position and the nucleotide sequence of the promoter revealed two AT-rich sequences also present at the equivalent position in the region 3 promoter. These may represent sites for the co-ordinated regulation of the conserved regions 1 and 3. Two potential IHF binding sites were also identified near the region 1 promoter. The region 1 transcript included an additional gene, kpsF, previously thought to be outside the capsule cluster. This encoded a 35.6 kDa KpsF protein with a predicted amino acid sequence 95% identical to KpsF from E. coli K1 and also homologous with GutQ, ORF328 and an hypothetical open reading frame from Haemophilus influenzae. KpsF is not essential for capsule production and no regulatory role could be established. An intragenic, Rho-dependent transcriptional terminator was discovered within kpsF and may link transcription of region 1 with the physiological status of the cell. Group II capsules are expressed at 37C but not 18C and region 1 was regulated at the level of transcription, with transcripts barely detectable at 18C by Northern blotting or RNase protection. The temperature-regulation of region 1 was unaffected by mutations in regulatory genes known to control the expression of other temperature-dependent virulence factors. A mutation in rfaH, which affects group II capsule expression also had no effect on region 1 expression.