A "gain of function" mutation in a protein mediates production of novel modified nucleosides.
The mutation sufY204 mediates suppression of a +1 frameshift mutation in the histidine operon of Salmonella enterica serovar Typhimurium and synthesis of two novel modified nucleosides in tRNA. The sufY204 mutation, which results in an amino-acid substitution in a protein, is, surprisingly, dominant over its wild-type allele and thus it is a "gain of function" mutation. One of the new nucleosides is 5-methylaminomethyl-2-thiouridine (mnm(5)s(2)U34) modified by addition of a C(10)H(17) side chain of unknown structure. Increased amounts of both nucleosides in tRNA are correlated to gene dosage of the sufY204 allele, to an increased efficiency of frameshift suppression, and to a decreased amount of the wobble nucleoside mnm(5)s(2)U34 in tRNA. Purified tRNA(Gln)(cmnm(5)s(2)UUG) in the mutant strain contains a modified nucleoside similar to the novel nucleosides and the level of aminoacylation of tRNA(Gln)(cmnm(5)s(2)UUG) was reduced to 26% compared to that found in the wild type (86%). The results are discussed in relation to the mechanism of reading frame maintenance and the evolution of modified nucleosides in tRNA.
Chen
Peng
P
Department of Molecular Biology, Umeå University, S-901 87 Umeå, Sweden.
Crain
Pamela F
PF
Näsvall
S Joakim
SJ
Pomerantz
Steven C
SC
Björk
Glenn R
GR
D019943:Amino Acid Substitution; D016368:Frameshift Mutation; D016153:Genes, Suppressor; D007763:Lac Operon / Q000235:genetics; D009705:Nucleosides / Q000096:biosynthesis* / Q000737:chemistry; D009876:Operon; D012343:RNA, Transfer / Q000737:chemistry / Q000235:genetics; D012486:Salmonella typhimurium / Q000235:genetics / Q000378:metabolism; D064586:Selenic Acid; D018036:Selenium Compounds / Q000378:metabolism; D021241:Spectrometry, Mass, Electrospray Ionization; D046249:Transfer RNA Aminoacylation / Q000235:genetics / Q000502:physiology
D009705:Nucleosides; D018036:Selenium Compounds; D012343:RNA, Transfer; D064586:Selenic Acid