InterPro domain: IPR036225

This entry represents the N-terminal helical bundle domain of the 54kDa SRP54 component, a GTP-binding protein that interacts with the signal sequence when it emerges from the ribosome. SRP54 of the signal recognition particle has a three-domain structure: an N-terminal helical bundle domain, a GTPase domain, and the M-domain that binds the 7s RNA and also binds the signal sequence. The extreme C-terminal region is glycine-rich and lower in complexity and poorly conserved between species.

Other proteins with this domain include signal recognition particle receptor alpha subunit (docking protein), an integral membrane GTP-binding protein which ensures (in conjunction with SRP) the correct targeting of nascent secretory proteins to the endoplasmic reticulum membrane; and bacterial FtsY protein, which is believed to play a similar role to that played by the eukaryotic docking protein.