Comparative studies on the '5'-cap' and in vitro translational activity of cytoplasmic and nuclear poly A(+) RNA1.
The translational activities of cytoplasmic poly A(+)RNA of normal rat liver and Novikoff hepatoma cells in the wheat germ cell free system were found to be approximately 15-20 times greater than tose of the corresponding nuclear poly A(+) RNA. The translationsl activities were 85 and 62 pmoles 3H-leucine incorporated/micron g cytoglasmic poly A(+) RNA for the liver and tumor respectively and 3-4 pmoles 3H-leucine incoporated/micron g nuclear poly A(+)RNA. Inasmuch as intergity of the '5'-cap' of mRNA is essential for its translational activity, quantitative comparisons were made of its content in these RNA fractions. Of the total 32P incorporated into the tumor cytoplasmic poly A(+) RNA, 0.41% was in the '5'-cap'; in nuclear poly A(+) RNA, the '5'-cap' contained 0.11%. After periodate oxidation and labeling with KB3H4, m7 guanosine, the 5'-terminal nucleoside in both liver and Novikoff hepatoma nuclear poly A(+) RNA contained approximately 20% as much isotope as in the cytoplasmic poly A(+) RNA. These results suggest the lower translational activity of nuclear poly A(+) RNA is partly related to its lower content of the '5'-cap'. Molecular selection of poly A(+) RNA for transport out of the nucleus or further cytoplasmic processing may account for the higher percentage of the '5-cap' and the greater translational activity of the cytoplasmic poly A(+) RNA. During these studies, it was also found that the m7 guanosine of the '5'-cap' was not removed during translation of the mRNA in the wheat germ system; this result suggests that the '5'-cap' may associate with allosteric binding sites of initiation factor(s).
D000818:Animals; D006528:Carcinoma, Hepatocellular / Q000378:metabolism; D002467:Cell Nucleus / Q000378:metabolism*; D002499:Centrifugation, Density Gradient; D003593:Cytoplasm / Q000378:metabolism; D007700:Kinetics; D008099:Liver / Q000378:metabolism*; D008113:Liver Neoplasms / Q000378:metabolism; D008297:Male; D008970:Molecular Weight; D009374:Neoplasms, Experimental / Q000378:metabolism; D011061:Poly A / Q000378:metabolism; D014176:Protein Biosynthesis; D012313:RNA / Q000302:isolation & purification / Q000378:metabolism*; D012334:RNA, Neoplasm / Q000302:isolation & purification / Q000378:metabolism; D051381:Rats
D012334:RNA, Neoplasm; D011061:Poly A; D012313:RNA