title: Function of the repeating homologous sequences in nucleic acid binding domain of ribosomal protein S1.
abstract: Ribosomal protein S1 contains in its RNA binding domain four repeating, homologous stretches of sequences. Its functionally active mutant form m1-S1 [Subramanian, A.R., & Mizushima, S. (1979) J. Biol. Chem. 254, 4309] contains only three repeating stretches. In order to assess the functional importance of this repeating sequence, we cleaved S1 at its reactive SH group on Cys-349 and isolated a fragment (S1-F4) that has lost two of the homologous stretches but retains all other essential elements. We find that ribosomes reconstituted with S1-F4 instead of S1 are functionally active in translating poly(U) and poly(A) but totally inactive in translating phage MS2 RNA. The significance of this result is discussed vis-à-vis the initiation step in translating natural mRNA, and a functional role for the tetrarepeat of S1 is suggested.
mesh_terms: D000595:Amino Acid Sequence; D001665:Binding Sites; D003553:Cystine / Q000032:analysis; D004926:Escherichia coli; D005779:Immunodiffusion; D010446:Peptide Fragments / Q000302:isolation & purification; D012329:RNA, Bacterial / Q000378:metabolism; D012269:Ribosomal Proteins / Q000032:analysis* / Q000378:metabolism
chemical_list: D010446:Peptide Fragments; D012329:RNA, Bacterial; D012269:Ribosomal Proteins; C015494:ribosomal protein S1; D003553:Cystine