title: S1 and KH domains of polynucleotide phosphorylase determine the efficiency of RNA binding and autoregulation.
abstract: To better understand the roles of the KH and S1 domains in RNA binding and polynucleotide phosphorylase (PNPase) autoregulation, we have identified and investigated key residues in these domains. A convenient pnp::lacZ fusion reporter strain was used to assess autoregulation by mutant PNPase proteins lacking the KH and/or S1 domains or containing point mutations in those domains. Mutant enzymes were purified and studied by using in vitro band shift and phosphorolysis assays to gauge binding and enzymatic activity. We show that reductions in substrate affinity accompany impairment of PNPase autoregulation. A remarkably strong correlation was observed between β-galactosidase levels reflecting autoregulation and apparent KD values for the binding of a model RNA substrate. These data show that both the KH and S1 domains of PNPase play critical roles in substrate binding and autoregulation. The findings are discussed in the context of the structure, binding sites, and function of PNPase.
authors: Department of Biochemistry and Molecular Biology, Life Sciences Centre, The University of British Columbia, Vancouver, BC, Canada.
authors: Alexander G
authors: AG
authors: Wong
authors: Kristina L
authors: KL
authors: McBurney
authors: Katharine J
authors: KJ
authors: Thompson
authors: Leigh M
authors: LM
authors: Stickney
authors: George A
authors: GA
authors: Mackie
mesh_terms: D004926:Escherichia coli / Q000737:chemistry / Q000201:enzymology* / Q000235:genetics; D029968:Escherichia coli Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D015971:Gene Expression Regulation, Enzymologic; D006706:Homeostasis; D007700:Kinetics; D011117:Polyribonucleotide Nucleotidyltransferase / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D012329:RNA, Bacterial / Q000235:genetics / Q000378:metabolism*
chemical_list: D029968:Escherichia coli Proteins; D012329:RNA, Bacterial; D011117:Polyribonucleotide Nucleotidyltransferase