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 Hal obacterium salinarum. The fla gene cluster is located upstream of the flage llin genes flgB1-3 and oriented in the opposite direction. It consists of n ine open reading frames (ORFs): htpIX, a member of the halobacterial transd ucer 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, f laK shows similarities to bacterial genes involved in the regulation of fla gellar 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 r elation to members of the bacterial pili type IV-type II secretion protein superfamily. Reverse transcription-polymerase chain reaction (RT-PCR) analy sis revealed that the genes flaE to flaK are transcribed into one polycistr onic message. In frame deletion mutants of flal were generated by gene repl acement. The deletion strain lacks motility and belongs to the fla(-) mutan t class, indicating that it is deficient in flagellar biogenesis. The overa ll amount of flagellin protein in Delta flal cells is reduced, although tra nscription of the flagellin genes is unaffected. Therefore, the flal gene p roduct is involved in the biosynthesis, transport or assembly of flagella i n H. salinarum.