title: Hfq stimulates the activity of the CCA-adding enzyme.
abstract: BACKGROUND
  The bacterial Sm-like protein Hfq is known as an important regulator involved in many reactions of RNA metabolism. A prominent function of Hfq is the stimulation of RNA polyadenylation catalyzed by E. coli poly(A) polymerase I (PAP). As a member of the nucleotidyltransferase superfamily, this enzyme shares a high sequence similarity with an other representative of this family, the tRNA nucleotidyltransferase that synthesizes the 3'-terminal sequence C-C-A to all tRNAs (CCA-adding enzyme). Therefore, it was assumed that Hfq might not only influence the poly(A) polymerase in its specific activity, but also other, similar enzymes like the CCA-adding enzyme.
  
  
  RESULTS
  Based on the close evolutionary relation of these two nucleotidyltransferases, it was tested whether Hfq is a specific modulator acting exclusively on PAP or whether it also influences the activity of the CCA-adding enzyme. The obtained data indicate that the reaction catalyzed by this enzyme is substantially accelerated in the presence of Hfq. Furthermore, Hfq binds specifically to tRNA transcripts, which seems to be the prerequisite for the observed effect on CCA-addition.
  
  
  CONCLUSIONS
  The increase of the CCA-addition in the presence of Hfq suggests that this protein acts as a stimulating factor not only for PAP, but also for the CCA-adding enzyme. In both cases, Hfq interacts with RNA substrates, while a direct binding to the corresponding enzymes was not demonstrated up to now (although experimental data indicate a possible interaction of PAP and Hfq). So far, the basic principle of these stimulatory effects is not clear yet. In case of the CCA-adding enzyme, however, the presented data indicate that the complex between Hfq and tRNA substrate might enhance the product release from the enzyme.
authors.affiliation: Institute for Biochemistry, University of Leipzig, Brüderstr, 34, 04103 Leipzig, Germany. mscheibe@uni-leipzig.de
authors.forename: Marion
authors.initials: M
authors.lastname: Scheibe
authors.forename: Sonja
authors.initials: S
authors.lastname: Bonin
authors.forename: Eliane
authors.initials: E
authors.lastname: Hajnsdorf
authors.forename: Heike
authors.initials: H
authors.lastname: Betat
authors.forename: Mario
authors.initials: M
authors.lastname: Mörl
mesh_terms: D001483:Base Sequence; D004789:Enzyme Activation; D029968:Escherichia coli Proteins / Q000378:metabolism / Q000502:physiology*; D035001:Host Factor 1 Protein / Q000502:physiology*; D007700:Kinetics; D011062:Polynucleotide Adenylyltransferase / Q000378:metabolism; D011485:Protein Binding; D012316:RNA Nucleotidyltransferases / Q000378:metabolism*; D012343:RNA, Transfer / Q000378:metabolism; D013379:Substrate Specificity
chemical_list: D029968:Escherichia coli Proteins; C087373:Hfq protein, E coli; D035001:Host Factor 1 Protein; D012343:RNA, Transfer; D012316:RNA Nucleotidyltransferases; C023198:tRNA nucleotidyltransferase; D011062:Polynucleotide Adenylyltransferase; C063643:pcnB protein, E coli