Component of the signal recognition particle (SRP) complex, a ribonucleoprotein complex that mediates the cotranslational targeting of secretory and membrane proteins to the endoplasmic reticulum (ER) (By similarity). As part of the SRP complex, associates with the SRP receptor (SR) component SRPRA to target secretory proteins to the endoplasmic reticulum membrane (By similarity). Binds to the signal sequence of presecretory proteins when they emerge from the ribosomes (By similarity). Displays basal GTPase activity, and stimulates reciprocal GTPase activation of the SR subunit SRPRA (By similarity). Forms a guanosine 5'-triphosphate (GTP)-dependent complex with the SR subunit SRPRA (By similarity). SR compaction and GTPase mediated rearrangement of SR drive SRP-mediated cotranslational protein translocation into the ER (By similarity). Requires the presence of SRP9/SRP14 and/or SRP19 to stably interact with RNA (By similarity). Plays a role in proliferation and differentiation of granulocytic cells, neutrophils migration capacity and exocrine pancreas development (By similarity). GTP + H2O = GDP + H(+) + phosphate Component of a signal recognition particle (SRP) complex that consists of a 7SL RNA molecule of 300 nucleotides and six protein subunits: SRP72, SRP68, SRP54, SRP19, SRP14 and SRP9 (By similarity). Interacts with RNPS1 (By similarity). Interacts with the SRP receptor subunit SRPRA (By similarity). The NG domain, also named G domain, is a special guanosine triphosphatase (GTPase) domain, which binds GTP and forms a guanosine 5'-triphosphate (GTP)-dependent complex with a homologous NG domain in the SRP receptor subunit SRPRA (By similarity). The two NG domains undergo cooperative rearrangements upon their assembly, which culminate in the reciprocal activation of the GTPase activity of one another (By similarity). SRP receptor compaction upon binding with cargo-loaded SRP and GTPase rearrangement drive SRP-mediated cotranslational protein translocation into the ER (By similarity). The M domain binds the 7SL RNA in presence of SRP19 and binds the signal sequence of presecretory proteins. Belongs to the GTP-binding SRP family. SRP54 subfamily.