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  • Title: HeLa cell cytoplasmic mRNA contains three classes of sequences: predominantly poly(A)-free, predominantly poly(A)-containing and bimorphic.
    Author: Milcarek C.
    Journal: Eur J Biochem; 1979 Dec 17; 102(2):467-76. PubMed ID: 527589.
    Abstract:
    The mRNA species which exist in the HeLa cell polyribisomes in a form devoid of A sequences longer than 8 nucleotides constitute the poly(A)-free class of mRNA. The rapidly labelled component of this mRNA class shares no measurable sequence homology with poly(A)-containing RNA. If poly(A)-free mRNA larger than 12 S labelled for 2 h in vivo is hybridized with total cellular DNA, it hybridizes primarily with single-copy DNA. When a large excess of steady poly(A)-containing RNA is added before hybridization of labelled poly(A)-free RNA, no inhibition of hybridization occurs. This indicates the existence of a class of poly(A)-free mRNA with no poly(A)-containing counterpart. Some mRNA species can exist solely as poly(A)-containing mRNAs. These mRNAs in HeLa cells are found almost exclusively in the mRNA species present only a few times per cell (scarce sequences). Some mRNA species can exist in two forms, poly(A)containing and lacking, as evidenced by the translation data in vitro of Kaufmann et al. [Proc. Natl Acad. Sci. U.S.A. 74, 4801--4805 (1977)]. In addition, if cDNA to total poly(A)-containing mRNA is fractionated into abundant and scarce classes, 47% of the scarce class cDNA can be readily hybridized with poly(A)-free mRNA. 10% of the abundant cDNA to poly(A)-containing mRNA will hybridize with poly(A)-free sequences very rapidly while the other 90% hybridize 160 times more slowly, indicating two very different frequency distributions. The cytoplasmic metabolism of these three distinct mRNA classes is discussed.
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