Deficiency of 1-methylguanosine in tRNA from Salmonella typhimurium induces frameshifting by quadruplet translocation.
The trmD gene encodes the tRNA(m1G37)methyltransferase, which methylates guanosine (G) to 1-methylguanosine (m1G) at position 37 of tRNAs that read CUN (leucine), CCN (proline), and CGG (arginine) codons. A mutant, trmD3, has previously been isolated, which at high temperature lacks m1G in tRNA, and this deficiency was correlated with a +1 frameshifting activity. In this study, the mechanism of this trmD3-induced frameshift involving mutant tRNA(Pro) and tRNA(Leu) species has been investigated. Potential frameshifting sites for proline tRNAs, CCC-N, were efficiently suppressed in the mutant strain. Hybrid beta-galactosidases encoded by plasmid constructs containing the sites CCC-U and CCC-A were subjected to amino-terminal sequencing. The protein sequences demonstrated that a quadruplet translocation had occurred and that a proline was inserted at these sites, suggesting that a tRNA(Pro) deficient in m1G is the frameshifting agent. Therefore, a mechanism involving a quadruplet codon-anticodon interaction is favoured for trmD3-dependent +1 frameshifting. Of the four potential sites for tRNA(Leu) (CCU-N), two, CCU-U and CCU-C, were significantly suppressed in the trmD3 mutant. Thus, species of tRNA(Leu) may also act as +1 frameshift suppressors. No -1 frameshifting activity was found with the trmD3 mutant.
Hagervall
T G
TG
Department of Microbiology, University of Umeå, Sweden.
Tuohy
T M
TM
Atkins
J F
JF
Björk
G R
GR
D000595:Amino Acid Sequence; D001483:Base Sequence; D016368:Frameshift Mutation / Q000235:genetics*; D006151:Guanosine / Q000031:analogs & derivatives / Q000172:deficiency; D008969:Molecular Sequence Data; D012329:RNA, Bacterial / Q000235:genetics*; D012343:RNA, Transfer / Q000235:genetics*; D012356:RNA, Transfer, Leu / Q000235:genetics; D012361:RNA, Transfer, Pro / Q000235:genetics; D012486:Salmonella typhimurium / Q000235:genetics*; D013489:Suppression, Genetic / Q000235:genetics*; D001616:beta-Galactosidase / Q000235:genetics; D001618:beta-Lactamases / Q000235:genetics
D012329:RNA, Bacterial; D012356:RNA, Transfer, Leu; D012361:RNA, Transfer, Pro; D006151:Guanosine; C020770:1-methylguanosine; D012343:RNA, Transfer; D001616:beta-Galactosidase; D001618:beta-Lactamases