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Journal of Bacteriology, October 2007, p. 7024-7031, Vol. 189, No. 19
0021-9193/07/$08.00+0     doi:10.1128/JB.00710-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Alterations in the Two Globular Domains or in the Connecting -Helix of Bacterial Ribosomal Protein L9 Induces +1 Frameshifts

Ramune Leipuviene and Glenn R. Björk^*

Department of Molecular Biology, Umeå University, S-90187 Umeå, Sweden

Received 3 May 2007/ Accepted 17 July 2007

The ribosomal 50S subunit protein L9, encoded by the gene rplI, is an elongated protein with an -helix connecting the N- and C-terminal globular domains. We isolated rplI mutants that suppress the +1 frameshift mutation hisC3072 in Salmonella enterica serovar Typhimurium. These mutants have amino acid substitutions in the N-terminal domain (G24D) or in the C-terminal domain (I94S, A102D, G126V, and F132S) of L9. In addition, different one-base deletions in rplI altered either the final portion of the C terminus or removed the C-terminal domain with or without the connecting -helix. An alanine-to-proline substitution at position 59 (A59P), which breaks the -helix between the globular domains, induced +1 frameshifting, suggesting that the geometrical relationship between the N and C domains is important to maintain the reading frame. Except for the alterations G126V in the C terminus and A59P in the connecting -helix, our results confirm earlier results obtained by using the phage T4 gene 60-based system to monitor bypassing. The way rplI mutations suppress various frameshift mutations suggests that bypassing of many codons from several takeoff and landing sites occurred instead of a specific frameshift forward at overlapping codons.

Published ahead of print on 27 July 2007.

Present address: Children's Hospital Oakland Research Institute, 5700 Martin Luther King, Jr. Way, Oakland, CA 94609.