srb: a Bacillus subtilis gene encoding a homologue of the alpha-subunit of the mammalian signal recognition particle receptor.

We cloned a Bacillus subtilis gene (srb) encoding a homologue of the mammalian signal recognition particle receptor alpha-subunit (SR alpha). The gene is 987 bp in length and encodes a 329-amino acid protein. The deduced amino acid sequence of the protein shared 26.6, 36.2 and 49.7% identity with those of mammalian SR alpha, archaebacterial DP alpha and Escherichia coli FtsY, respectively. The protein contains three conserved GTP-binding elements like the other three SRP receptor proteins, though the N-terminal portion of the putative B. subtilis protein was shorter than the others. Secondary structure prediction showed than an amphipathic alpha-helix is positioned in the N-terminal region. A defect in srb inhibited cell growth and protein translocation.