Gene fliA encodes an alternative sigma factor specific for flagellar operons in Salmonella typhimurium

Abstract

Through genetic studies, the fliA gene product has been shown to regulate positively gene expression in late operons of the flagellar regulon in Salmonella typhimurium. In the present study, the fliA gene was cloned and sequenced. The fliA coding region consisted of 717 nucleotides beginning with the GTG initiation codon and the conserved sequence specific to promoters for flagellar operons was found to exist upstream of the coding region. The fliA gene product deduced from the nucleotide sequence was a protein with 239 amino acid residues and the calculated molecular mass was 27,470 dalton. The deduced amino acid sequence was homologous with that of sigma 28, a flagellar specific sigma factor of Bacillus subtilis. The fliA gene product was identified as a protein of molecular mass 29 kDa in the in vitro transcription-translation system, while three proteins of 29 kDa, 31 kDa and 32 kDa were found in the products programmed by the fliA gene in minicells and in maxicells. The 29 kDa FliA protein was purified from the FliA overproducing strain which carried the ptac-fliA fusion. This protein activated the in vitro synthesis of flagellin, the fliC gene product. RNA polymerase containing the purified FliA protein was shown to transcribe the fliC gene. These results indicate that FliA protein functions as an alternative sigma factor specific for S. typhimurium flagellar operons.

Characterization of the sigD transcription unit of Bacillus subtilis

“…3). (32) and WhiG (10). Identical residues in at least two of the three protein sequences are indicated in boldface type.…”

“…The cF factor of E. coli displays a promoter specificity similar to that of aD and has been shown to transcribe certain flagellar and chemotaxis genes in that organism (3). The gene for the uF factor was identified in S. typhimurium as being thefliA locus (32), part of a class of fla, che, and mot genes termed class II genes (13,14,22,23).…”

Structure and expression of the fliA operon of Salmonella typhimurium

“…These flagellar genes constitute at least 14 different operons, and most of them are clustered in four regions on the chromosome (Kutsukake et al, 1988;Macnab, 1996). Transcription of these operons forms a highly organized cascade called the flagellar regulon, and is coordinated with the flagellar assembly hierarchy (Kutsukake et al, 1990;Kutsukake & Iino, 1994). According to the relative positions in the transcriptional hierarchy, the flagellar operons are grouped into three classes, 1, 2 and 3.…”

“…Class 2 contains the operons responsible for formation of the flagellar basal structure, the hookbasal body complex. Class 2 also contains the fiiA gene, which encodes an alternative sigma factor, a ' ' , needed for class 3 expression (Ohnishi et al, 1990). Class 3 contains operons responsible for filament formation, flagellar rotation and chemotaxis.…”

“…Though the fliA gene product has been characterized extensively in S. typhimurium (Ohnishi et al, 1990;Kutsukake et al, 1994b), the entire structure and expression of the fliA operon have been less wellcharacterized in this organism. In the present work, we analysed the DNA sequence and transcriptional control of the fliA operon of S. typhimuriurn.…”