Binds to the signal sequence of presecretory protein when they emerge from the ribosomes and transfers them to TRAM (translocating chain-associating membrane protein). Signal recognition particle consists of a 7S RNA molecule of 300 nucleotides and six protein subunits: SRP72, SRP68, SRP54, SRP19, SRP14 and SRP9. Has a two domain structure: the G-domain binds GTP; the M-domain binds the 7S RNA in presence of SRP19 and also binds the signal sequence. Belongs to the GTP-binding SRP family. SRP54 subfamily. Sequencing errors.