Role of the 3'-poly(A) sequence in translational regulation of mRNAs in Xenopus laevis oocytes.
We investigated the effect of 3'-noncoding and poly(A) sequences on the translation and stability of membrane-bound mRNA (maize zein) and free mRNA (Xenopus beta-globin) by injecting SP6 transcripts into stage 6 Xenopus oocytes. With zein mRNA, the presence or absence of a 3'-noncoding or poly(A) sequence had little effect on mRNA stability over 24 h, and the 3'-noncoding sequence played essentially no role in mRNA translation. With short periods of incubation, e.g. 1-2 h, the presence or absence of a poly(A) tail also had little effect on zein mRNA translation; but after longer periods, translation of the poly(A-) mRNA was significantly reduced. A similar pattern of mRNA translation was observed for poly(A+) and poly(A-) Xenopus beta-globin mRNAs. These differences in translational efficiency correlated with the formation of maximally loaded polysomes (seven-eight ribosomes/mRNA) for the poly(A+) zein mRNA and a failure to form large polysomes with the poly(A-) zein mRNA. These results are consistent with a model in which the 3'-poly(A) sequence of mRNAs facilitates reinitiation of ribosomes during protein synthesis.
Galili
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Department of Botany and Plant Pathology, Purdue University, West Lafayette, Indiana 47907.
Kawata
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Smith
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Larkins
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BA
D000818:Animals; D001483:Base Sequence; D004247:DNA; D004274:DNA, Recombinant; D005260:Female; D005914:Globins / Q000096:biosynthesis / Q000235:genetics*; D009865:Oocytes / Q000378:metabolism*; D011061:Poly A / Q000378:metabolism; D014176:Protein Biosynthesis; D012333:RNA, Messenger / Q000235:genetics*; D012270:Ribosomes / Q000378:metabolism; D014982:Xenopus laevis; D015028:Zein / Q000096:biosynthesis / Q000235:genetics*
D004274:DNA, Recombinant; D012333:RNA, Messenger; D011061:Poly A; D005914:Globins; D004247:DNA; D015028:Zein