This superfamily represents the RNA-binding domain of SRP68 subunit of the signal recognition particle (SRP) complex. This large ribonucleoprotein complex, consisting of six proteins (SRP9, SRP14, SRP19, SRP54, SRP68, and SRP72) and a 7SL-RNA plays a role in guiding the emerging proteins designed for the membrane towards the translocation pore. The two largest subunits, SRP68 and SRP72, form a stable heterodimer, which is required for sorting secretory proteins PMID:19693936. SRP68 binds to SRP RNA directly, while SRP72 binds the SRP RNA largely via non-specific electrostatic interaction. The binding of SRP72 with SRP RNA enhances the affinity of SRP68 for the RNA.

This entry represents the SRP68-RBD (RNA-binding domain), a tetratricopeptide-like module that binds to a RNA three-way junction, bends the RNA, and inserts an alpha-helical arginine-rich motif (ARM) into the major groove. The ARM opens the conserved 5f RNA loop, which in ribosome-bound SRP establishes a contact to ribosomal RNA. Its function is predicted to involve protein translocation.

PFAM:PF16969, INTERPRO:IPR026258,DOI:10.1126/science.1249094,DOI:10.1093/nar/gkw1124