The fla gene cluster is involved in the biogenesis of flagella in Halobacterium salinarum

In this study, a flagella-related protein gene cluster is described for Halobacterium salinarum. The fla gene cluster is located upstream of the flagellin genes flgB1-3 and oriented in the opposite direction. It consists of nine open reading frames (ORFs): htpIX, a member of the halobacterial transducer protein gene family, and the genes flaD-K. The genes flaD, E, G, H, I and J share high homologies with genes from other Archaea. Interestingly, flaK shows similarities to bacterial genes involved in the regulation of flagellar synthesis. The ORFs of flaH, flal and flaK contain sequences coding for nucleotide binding sites. Furthermore, flal contains a motif called the bacterial type II secretion protein E signature, indicating a functional relation to members of the bacterial pili type IV-type II secretion protein superfamily. Reverse transcription-polymerase chain reaction (RT-PCR) analysis revealed that the genes flaE to flaK are transcribed into one polycistronic message. In frame deletion mutants of flal were generated by gene replacement. The deletion strain lacks motility and belongs to the fla^- mutant class, indicating that it is deficient in flagellar biogenesis. The overall amount of flagellin protein in Δflal cells is reduced, although transcription of the flagellin genes is unaffected. Therefore, the flal gene product is involved in the biosynthesis, transport or assembly of flagella in H. salinarum.