Determinants on tmRNA for initiating efficient and precise trans-translation: some mutations upstream of the tag-encoding sequence of Escherichia coli tmRNA shift the initiation point of trans-translation in vitro.
tmRNA facilitates a novel translation, trans-translation, in which a ribosome can switch between translation of a truncated mRNA and the tmRNA's tag sequence. The mechanism underlying resumption of translation at a definite position is not known. In the present study, the effects of mutations around the initiation point of the tag-encoding sequence of Escherichia coli tmRNA on the efficiency and the frame of tag translation were assessed by measuring the incorporations of several amino acids into in vitro poly (U)-dependent tag-peptide synthesis. One-nucleotide insertions within the tag-encoding region did not shift the frame of tag translation. Any 1-nt deletion within the span of -5 to -1, but not at -6, made the frame of tag translation heterologous. Positions at which a single base substitution caused a decrease of trans-translation efficiency were concentrated within the span of -4 to -2. In particular, an A-4 to C-4 mutation seriously damaged the trans-translation, although this mutant retained normal aminoacylation and ribosome-binding abilities. A possible stem and loop structure around this region was not required for transtranslation. It was concluded that the tag translation requires the primary sequence encompassing -6 to +11, in which the central 3 nt, A-4, G-3, and U-2, play an essential role. It was also found that several base substitutions within the span of -6 to -1 extensively shifted the tag-initiation point by -1.
Lee
S
S
Department of Biochemistry and Biotechnology, Faculty of Agriculture and Life Science, Hirosaki University, Japan.
Ishii
M
M
Tadaki
T
T
Muto
A
A
Himeno
H
H
D000215:Acylation; D001483:Base Sequence; D004926:Escherichia coli / Q000235:genetics*; D008969:Molecular Sequence Data; D009154:Mutation; D009690:Nucleic Acid Conformation; D014176:Protein Biosynthesis / Q000235:genetics*; D012329:RNA, Bacterial / Q000737:chemistry / Q000378:metabolism* / Q000502:physiology
D012329:RNA, Bacterial; C096222:tmRNA