The Bacillus subtilis SRP54 homologue, Ffh, has an intrinsic GTPase activity and forms a ribonucleoprotein complex with small cytoplasmic RNA in vivo.

B. subtilis Ffh is a homologue of SRP54, which is one component of the mammalian signal recognition particle. B. subtilis Ffh was expressed in E. coli as a derivative with a hexa histidine tag at the COOH terminus and purified to near homogeneity. The purified Ffh had intrinsic GTPase activity as predicted from its amino acid sequence. Using antiserum against Ffh, we also demonstrated that B. subtilis Ffh forms a complex with scRNA which is a B subtilis homologue of the RNA component of SRP in vivo, and that half of the resulting complex is found in the peripheral fraction of the cytoplasmic membrane where the initiation of protein translocation occurs. These findings provide evidence of a ribonucleoprotein complex in B. subtilis, reminiscent of SRP.