Conserved small mRNA with an unique, extended Shine-Dalgarno sequence.
Up to now, very small protein-coding genes have remained unrecognized in sequenced genomes. We identified an mRNA of 165 nucleotides (nt), which is conserved in Bradyrhizobiaceae and encodes a polypeptide with 14 amino acid residues (aa). The small mRNA harboring a unique Shine-Dalgarno sequence (SD) with a length of 17 nt was localized predominantly in the ribosome-containing P100 fraction of Bradyrhizobium japonicum USDA 110. Strong interaction between the mRNA and 30S ribosomal subunits was demonstrated by their co-sedimentation in sucrose density gradient. Using translational fusions with egfp, we detected weak translation and found that it is impeded by both the extended SD and the GTG start codon (instead of ATG). Biophysical characterization (CD- and NMR-spectroscopy) showed that synthesized polypeptide remained unstructured in physiological puffer. Replacement of the start codon by a stop codon increased the stability of the transcript, strongly suggesting additional posttranscriptional regulation at the ribosome. Therefore, the small gene was named rreB (ribosome-regulated expression in Bradyrhizobiaceae). Assuming that the unique ribosome binding site (RBS) is a hallmark of rreB homologs or similarly regulated genes, we looked for similar putative RBS in bacterial genomes and detected regions with at least 16 nt complementarity to the 3'-end of 16S rRNA upstream of sORFs in Caulobacterales, Rhizobiales, Rhodobacterales and Rhodospirillales. In the Rhodobacter/Roseobacter lineage of α-proteobacteria the corresponding gene (rreR) is conserved and encodes an 18 aa protein. This shows how specific RBS features can be used to identify new genes with presumably similar control of expression at the RNA level.
a Institute of Microbiology and Molecular Biology, Justus-Liebig-University , Gießen , Germany.
Julia
J
Hahn
a Institute of Microbiology and Molecular Biology, Justus-Liebig-University , Gießen , Germany.
Sebastian
0000-0001-7021-1741
S
Thalmann
a Institute of Microbiology and Molecular Biology, Justus-Liebig-University , Gießen , Germany.|b A.N. Belozersky Institute of Physico-Chemical Biology, M.V. Lomonosov Moscow State University , Leninskye Gory 1, Moscow , Russia.
Anzhela
A
Migur
c Institut für Bio- und Geowissenschaften, IBG-1: Biotechnologie , Forschungszentrum Jülich , Germany.
Raphael Freiherr
RF
von Boeselager
d Institut für Organische Chemie und Chemische Biologie, Center for Biomolecular Magnetic Resonance (BMRZ), Johann Wolfgang Goethe-Universität , Frankfurt am Main , Germany.
Nina
N
Kubatova
b A.N. Belozersky Institute of Physico-Chemical Biology, M.V. Lomonosov Moscow State University , Leninskye Gory 1, Moscow , Russia.
Elena
E
Kubareva
d Institut für Organische Chemie und Chemische Biologie, Center for Biomolecular Magnetic Resonance (BMRZ), Johann Wolfgang Goethe-Universität , Frankfurt am Main , Germany.
Harald
H
Schwalbe
a Institute of Microbiology and Molecular Biology, Justus-Liebig-University , Gießen , Germany.
Elena
0000-0001-7270-3168
E
Evguenieva-Hackenberg
D001483:Base Sequence; D020369:Bradyrhizobium / Q000235:genetics* / Q000378:metabolism; D003001:Cloning, Molecular; D017124:Conserved Sequence; D015964:Gene Expression Regulation, Bacterial; D014176:Protein Biosynthesis; D012323:RNA Processing, Post-Transcriptional; D012329:RNA, Bacterial / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics* / Q000378:metabolism*; D054680:Ribosome Subunits, Small, Bacterial / Q000378:metabolism*
D012329:RNA, Bacterial; D012333:RNA, Messenger
α-proteobacteria; Bradyrhizobium; ribosomal binding site; ribosome; RNA stability; Shine-Dalgarno; small gene; small protein; sORF; translation initiation region