The cyanobacterial genome contains a single copy of the ffh gene encoding a homologue of the 54 kDa subunit of signal recognition particle

Cyanobacteria possess thylakoid membranes that differ in their protein composition from the cytoplasmic membrane. To study possible pathways of protein targeting to these membranes, we have investigated whether or not cyanobacteria have a homologue or homologues of the signal recognition particlelike chaperone Ffh. We have amplified a fragment of ffh by polymerase chain reaction and established that ffh is present as a single copy in the genomes of three cyanobacterial species. We have cloned and sequenced ffh from Synechococcus sp. PCC7942 and predict that Ffh functions as a ribonucleoprotein in cyanobacteria and chloroplasts.