RNA



Alterations in the peptidyltransferase and decoding domains of ribosomal RNA suppress mutations in the elongation factor G gene


HOMA  KOOSHA a1, DALE  CAMERON a1, KIM  ANDREWS a1, ALBERT E.  DAHLBERG a2 and PAUL E.  MARCH a1c1
a1 School of Microbiology and Immunology, The University of New South Wales, Sydney, 2052 Australia
a2 Department of Molecular and Cellular Biology and Biochemistry, Brown University, Providence, Rhode Island 02912, USA

Abstract

The translocation stage of protein synthesis is a highly conserved process in all cells. Although the components necessary for translocation have been delineated, the mechanism of this activity has not been well defined. Ribosome movement on template mRNA must allow for displacement of tRNA–mRNA complexes from the ribosomal A to P sites and P to E sites, while ensuring rigid maintenance of the correct reading frame. In Escherichia coli, translocation of the ribosome is promoted by elongation factor G (EF-G). To examine the role of EF-G and rRNA in translocation we have characterized mutations in rRNA genes that can suppress a temperature-sensitive (ts) allele of fusA, the gene in E. coli that encodes EF-G. This analysis was performed using the ts E. coli strain PEM100, which contains a point mutation within fusA. The ts phenotype of PEM100 can be suppressed by either of two mutations in the decoding region of the 16S rRNA when present in combination with a mutation at position 2058 in the peptidyltransferase domain of the 23S rRNA. Communication between these ribosomal domains is essential for coordinating the events of the elongation cycle. We propose a model in which EF-G promotes translocation by modulating this communication, thereby increasing the efficiency of this fundamental process.

(Received March 6 2000)
(Revised April 5 2000)
(Accepted May 19 2000)


Key Words: EF-G mutants; ribosomes; rRNA mutants; translocation.

Correspondence:
c1 Reprint requests to: Paul E. March, School of Microbiology and Immunology, High Street and Botany Road, The University of New South Wales, Sydney, 2052 Australia; e-mail: p.march@unsw.edu.au.