title: The activity of discrete fragments of ribosomal protein S1 in Q beta replicase function.
abstract: As a subunit of bacteriophage Q beta replicase, ribosomal protein S1 is required for tight binding of the enzyme to Q beta RNA and for the initiation of Q beta RNA transcription. To compare these properties of S1 with its functions in protein synthesis, we have reconstituted altered replicase enzymes by adding discrete fragments of S1 to Q beta replicase lacking S1 (R(-S1]. We show that the NH2-terminal region of S1 is required for S1 subunit interactions in replicase since a trypsin-resistant fragment (denoted S1-F1) lacking the NH2-terminal 31% of S1 is functionally inactive and does not seem to bind to R(-S1). Previous studies with S1-F1 indicated that this NH2-terminal region is required for S1 to bind to the ribosome. Our results also show that the COOH-terminal region of S1 is dispensable for S1's function in replicase because a mutant of S1 (m1-S1) lacking 21% of the COOH-terminal portion of the chain is as active as wild type S1 in replicase and binds to R(-S1) with comparable affinity. In protein synthesis, the mutant m1-S1 is known to substitute for S1 but is only about 75% as efficient as wild type S1.
mesh_terms: D004926:Escherichia coli / Q000201:enzymology* / Q000235:genetics; D005033:Ethylmaleimide / Q000378:metabolism; D007700:Kinetics; D011777:Q beta Replicase / Q000378:metabolism*; D012316:RNA Nucleotidyltransferases / Q000378:metabolism*; D012269:Ribosomal Proteins / Q000378:metabolism*; D012270:Ribosomes / Q000378:metabolism
chemical_list: D012269:Ribosomal Proteins; C015494:ribosomal protein S1; D011777:Q beta Replicase; D012316:RNA Nucleotidyltransferases; D005033:Ethylmaleimide