The heterodimeric subunit SRP9/14 of the signal recognition particle functions as permuted single polypeptide chain.
The targeting of nascent polypeptide chains to the endoplasmic reticulum is mediated by a cytoplasmic ribonucleoprotein, the signal recognition particle (SRP). The 9 kD (SRP9) and the 14 kD (SRP14) subunits of SRP are required to confer elongation arrest activity to the particle. SRP9 and SRP14 form a heterodimer which specifically binds to SRP RNA. We have constructed cDNAs that encode single polypeptide chains comprising SRP9 and SRP14 sequences in the two possible permutations linked by a 17 amino acid peptide. We found that both fusion proteins specifically bound to SRP RNA as monomeric molecules folded into a heterodimer-like structure. Our results corroborate the previous hypothesis that the authentic heterodimer binds to SRP RNA in equimolar ratio. In addition, both fusion proteins conferred elongation arrest activity to SRP(-9/14), which lacks this function, and one fusion protein could functionally replace the heterodimer in the translocation assay. Thus, the normal N-and C-termini of both proteins have no essential role in folding, RNA-binding and in mediating the biological activities. The possibility to express the heterodimeric complex as a single polypeptide chain facilitates the analysis of its functions and its structure in vivo and in vitro.
Bovia
F
F
Département de Biologie Cellulaire, Université de Genève, Switzerland.
Bui
N
N
Strub
K
K
D000595:Amino Acid Sequence; D003001:Cloning, Molecular; D004721:Endoplasmic Reticulum / Q000378:metabolism; D004926:Escherichia coli / Q000378:metabolism; D008969:Molecular Sequence Data; D009692:Nucleic Acid Heteroduplexes; D012313:RNA / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000378:metabolism; D018271:Signal Recognition Particle / Q000737:chemistry* / Q000235:genetics
D009692:Nucleic Acid Heteroduplexes; D011993:Recombinant Fusion Proteins; D018271:Signal Recognition Particle; D012313:RNA