A cluster of flagellar genes of was identified and sequenced. This cluster comprises an operon, designated the flgK operon, which is initiated by a s-like promoter. The operon consists of (function unknown), (encoding HAP1), (encoding HAP3) and (function unknown), and maps at 185 kb on the chromosome. In other bacteria, the hook-associated proteins HAP1 and HAP3 connect the flagellar filament to the hook and are required for the last stage of flagellar assembly. Reverse transcriptase-PCR analysis indicated that through to are transcribed as a single mRNA, and primer extension analysis revealed that transcription of the operon is initiated by a s-like promoter upstream of Subcloning the flgK promoter element into a promoter probe cat vector revealed that the promoter element had strong activity in both and In addition, when this construct was transformed into a mutant of which lacked a functional flagellar-specific sfactor, the promoter was still functional. Based on these results, the promoter element of the flagellin gene ( hereafter referred to as ) was re-examined. encodes the flagellar filament protein, and a s-like promoter has been reported to be involved in the transcription of this gene. A transcriptional start point was found 1 bp downstream of the reported start site. The sequence around -10 and -35 are consistent with the presence of a s-like promoter in addition to the putative s-like promoter for In contrast to the promoter element, no activity was detected after subcloning a promoter element into the promoter probe Because a s-like promoter rather than a unique flagellar sigma factor is involved in the later stage of flagellar assembly, the regulation of flagellar genes is evidently different from that of other bacteria.


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