srb: a Bacillus subtilis Gene Encoding a Homologue of the -Subunit of the Mammalian Signal Recognition Particle Receptor

Abstract

We cloned a Bacillus subtilis gene ( srb ) encoding a homologue of the mammalian signal recognition particle receptor α-subunit (SRα). 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 SRα, archaebacterial DPα 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 that an amphipathic α-helix is positioned in the N-terminal region. A defect in srb inhibited cell growth and protein translocation.