INFORMOSOMAL AND POLYSOMAL MESSENGER RNA: DIFFERENTIAL KINETICS OF POLYADENYLATION AND NUCLEOCYTOPLASMIC TRANSPORT IN CHINESE HAMSTER CELLS

Author(s):  
M. Duane Enger ◽  
Helen L. Barrington ◽  
John L. Hanners
1981 ◽  
Vol 1 (2) ◽  
pp. 179-187 ◽  
Author(s):  
M Salditt-Georgieff ◽  
M M Harpold ◽  
M C Wilson ◽  
J E Darnell

The rate of synthesis in Chinese hamster cells of 5' cap structures, m7 GpppNmp, in large (greater than 700 bases) heterogeneous nuclear ribonucleic acid (RNA) molecules is two to three times faster than the synthesis of 3'-terminal polyadenylic acid segments. As judged by presence of caps, newly synthesized polysomal messenger RNA, exclusive of messenger RNA the size of histone messenger RNA, is more than 90% in the polyadenylated category. It appears, therefore, that between half and two-thirds of the long capped heterogeneous nuclear RNA molecules do not contribute a capped polysomal derivative to the cytoplasm. There are capped, nonpolysomal, non-polyadenylated molecules with a rapid turnover rate that fractionate with the cytoplasm. These metabolically unstable molecules either could represent leakage into the cytoplasm during fractionation or could truly spend a brief time in the cytoplasm before decay.


1981 ◽  
Vol 1 (2) ◽  
pp. 179-187
Author(s):  
M Salditt-Georgieff ◽  
M M Harpold ◽  
M C Wilson ◽  
J E Darnell

The rate of synthesis in Chinese hamster cells of 5' cap structures, m7 GpppNmp, in large (greater than 700 bases) heterogeneous nuclear ribonucleic acid (RNA) molecules is two to three times faster than the synthesis of 3'-terminal polyadenylic acid segments. As judged by presence of caps, newly synthesized polysomal messenger RNA, exclusive of messenger RNA the size of histone messenger RNA, is more than 90% in the polyadenylated category. It appears, therefore, that between half and two-thirds of the long capped heterogeneous nuclear RNA molecules do not contribute a capped polysomal derivative to the cytoplasm. There are capped, nonpolysomal, non-polyadenylated molecules with a rapid turnover rate that fractionate with the cytoplasm. These metabolically unstable molecules either could represent leakage into the cytoplasm during fractionation or could truly spend a brief time in the cytoplasm before decay.


1989 ◽  
Vol 9 (4) ◽  
pp. 1635-1641 ◽  
Author(s):  
S G Grant ◽  
R G Worton

We have investigated the genetic activation of the hprt (hypoxanthine-guanine phosphoribosyltransferase) gene located on the inactive X chromosome in primary and transformed female diploid Chinese hamster cells after treatment with the DNA methylation inhibitor 5-azacytidine (5azaCR). Mutants deficient in HPRT were first selected by growth in 6-thioguanine from two primary fibroblast cell lines and from transformed lines derived from them. These HPRT- mutants were then treated with 5azaCR and plated in HAT (hypoxanthine-methotrexate-thymidine) medium to select for cells that had reexpressed the hprt gene on the inactive X chromosome. Contrary to previous results with primary human cells, 5azaCR was effective in activating the hprt gene in primary Chinese hamster fibroblasts at a low but reproducible frequency of 2 x 10(-6) to 7 x 10(-6). In comparison, the frequency in independently derived transformed lines varied from 1 x 10(-5) to 5 x 10(-3), consistently higher than in the nontransformed cells. This increase remained significant when the difference in growth rates between the primary and transformed lines was taken into account. Treatment with 5azaCR was also found to induce transformation in the primary cell lines but at a low frequency of 4 x 10(-7) to 8 x 10(-7), inconsistent with a two-step model of transformation followed by gene activation to explain the derepression of hprt in primary cells. Thus, these results indicate that upon transformation, the hprt gene on the inactive Chinese hamster X chromosome is rendered more susceptible to action by 5azaCR, consistent with a generalized DNA demethylation associated with the transformation event or with an increase in the instability of an underlying primary mechanism of X inactivation.


1987 ◽  
Vol 15 (1) ◽  
pp. 30-32
Author(s):  
Michael Garle ◽  
Alison H. Hammond ◽  
Jeffrey R. Fry

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