Ribosomal protein S4 is a transcription factor with properties remarkably similar to NusA, a protein involved in both non-ribosomal and ribosomal RNA antitermination.
Escherichia coli ribosomal RNA (rRNA) operons contain antitermination motifs necessary for forming terminator-resistant transcription complexes. In preliminary work, we isolated 'antiterminating' transcription complexes and identified four new proteins potentially involved in rRNA transcription antitermination: ribosomal (r-) proteins S4, L3, L4 and L13. We show here that these r-proteins and Nus factors lead to an 11-fold increase in terminator read-through in in vitro transcription reactions. A significant portion of the effect was a result of r-protein S4. We show that S4 acted as a general antitermination factor, with properties very similar to NusA. It retarded termination and increased read-through at Rho-dependent terminators, even in the absence of the rRNA antiterminator motif. High concentrations of NusG showed reduced antitermination by S4. Like rrn antitermination, S4 selectively antiterminated at Rho-dependent terminators. Lastly, S4 tightly bound RNA polymerase in vivo. Our results suggest that, like NusA, S4 is a general transcription antitermination factor that associates with RNA polymerase during normal transcription and is also involved in rRNA operon antitermination. A model for key r-proteins playing a regulatory role in rRNA synthesis is presented.
Torres
M
M
Department of Molecular Biology and Microbiology, Tufts University School of Medicine, Boston, MA 02111, USA.
Condon
C
C
Balada
J M
JM
Squires
C
C
Squires
C L
CL
D001426:Bacterial Proteins / Q000502:physiology*; D001483:Base Sequence; D017931:DNA Primers; D012321:DNA-Directed RNA Polymerases / Q000378:metabolism; D029968:Escherichia coli Proteins; D010445:Peptide Elongation Factors; D011485:Protein Binding; D012313:RNA / Q000235:genetics*; D012269:Ribosomal Proteins / Q000378:metabolism / Q000502:physiology*; D014157:Transcription Factors / Q000378:metabolism / Q000502:physiology*; D014158:Transcription, Genetic / Q000502:physiology*; D035602:Transcriptional Elongation Factors
D001426:Bacterial Proteins; D017931:DNA Primers; D029968:Escherichia coli Proteins; D010445:Peptide Elongation Factors; D012269:Ribosomal Proteins; D014157:Transcription Factors; D035602:Transcriptional Elongation Factors; C068727:nusA protein, E coli; C031798:ribosomal protein S4; D012313:RNA; D012321:DNA-Directed RNA Polymerases