title: Prevention of cross-talk in conserved regulatory systems: identification of specificity determinants in RNA-binding anti-termination proteins of the BglG family.
abstract: Each family of signal transduction systems requires specificity determinants that link individual signals to the correct regulatory output. In Bacillus subtilis, a family of four anti-terminator proteins controls the expression of genes for the utilisation of alternative sugars. These regulatory systems contain the anti-terminator proteins and a RNA structure, the RNA anti-terminator (RAT) that is bound by the anti-terminator proteins. We have studied three of these proteins (SacT, SacY, and LicT) to understand how they can transmit a specific signal in spite of their strong structural homology. A screen for random mutations that render SacT capable to bind a RNA structure recognized by LicT only revealed a substitution (P26S) at one of the few non-conserved residues that are in contact with the RNA. We have randomly modified this position in SacT together with another non-conserved RNA-contacting residue (Q31). Surprisingly, the mutant proteins could bind all RAT structures that are present in B. subtilis. In a complementary approach, reciprocal amino acid exchanges have been introduced in LicT and SacY at non-conserved positions of the RNA-binding site. This analysis revealed the key role of an arginine side-chain for both the high affinity and specificity of LicT for its cognate RAT. Introduction of this Arg at the equivalent position of SacY (A26) increased the RNA binding in vitro but also resulted in a relaxed specificity. Altogether our results suggest that this family of anti-termination proteins has evolved to reach a compromise between RNA binding efficacy and specific interaction with individual target sequences.
authors.affiliation: Department of General Microbiology, Institute of Microbiology and Genetics, Georg-August University Göttingen, Grisebach strasse 8, D-37077 Göttingen, Germany.
authors.forename: Sebastian
authors.initials: S
authors.lastname: Hübner
authors.forename: Nathalie
authors.initials: N
authors.lastname: Declerck
authors.forename: Christine
authors.initials: C
authors.lastname: Diethmaier
authors.forename: Dominique
authors.initials: D
authors.lastname: Le Coq
authors.forename: Stephane
authors.initials: S
authors.lastname: Aymerich
authors.forename: Jörg
authors.initials: J
authors.lastname: Stülke
mesh_terms: D000595:Amino Acid Sequence; D001412:Bacillus subtilis / Q000235:genetics; D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D001665:Binding Sites; D008969:Molecular Sequence Data; D016296:Mutagenesis; D017434:Protein Structure, Tertiary; D012329:RNA, Bacterial / Q000737:chemistry / Q000378:metabolism; D016601:RNA-Binding Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D014157:Transcription Factors / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; C098955:LicT protein, Bacteria; D012329:RNA, Bacterial; D016601:RNA-Binding Proteins; C076894:SacY protein, Bacillus subtilis; D014157:Transcription Factors; C064872:antiterminator proteins, Bacteria