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S Shaila

Publications and source records attributed to S Shaila.

5 recordsLinked to original sources
PubMed1977

Impairment of reovirus mRNA methylation in extracts of interferon-treated Ehrilich ascites tumor cells: further characteristics of the phenomenon.

We reported earlier that the methylation of unmethylated reovirus mRNA (reo mRNAU) by the cellular methylating enzymes is impaired in extracts of uninfected, interferon-treated Ehrilich ascites tumor cells (S30INT). We find now that after the methylation of reo mRNAU has stopped in S30INT, the RNA can be reisolated and further methylated in an extract of control cells (S30C). Thus the impairment of methylation in S30INT cannot be due to cleavage or irreversible inactivation of reo mRNAU. Freshly added reo mRNAU can be methylated in S30INT in which the methylation of previously added reo mRNAU has stopped. This indicates that the impairment is due to the depletion of S-adenosylme thionine (the methyl donor), the accumulation of S-adenosylhomocysteine (an inhibitor of methylation), or the irreversible inactivation of reo mRNAU. Freshly added reo mRNAU can be methylated in S30INT in which the methylation of previously added reo mRNAU has stopped. This indicates that the impairment is not due to the depletion of S-adenosylmethionine (the methyl donor), the accumulation of S-adenoxylhomocysteine (an inhibitor of methylation), or the irreversible inactivation of the methylating enzymes. It may be due, however, to the unavailability of reo mRNAU for methylation. The extent of the impairment of reo mRNAU methylation in S30INT decreases with an increasing concentration of reo mRNAU but is not affected by added poly (U), ribosomal RNA, or encephalomyocarditis virus RNA (an mRNA that is probably not capped or methylated at its 5' end). The methylation of reo mRNAU is also impaired in an extract from cells that have not been treated with interferon but with the interferon inducer poly(I) - poly(C). The inhibitor is apparently a macromolecule that is inactivated during incubation. It decreases the methylation at the 7 position of the 5' terminal guanylate residue. In vitro, the rate of reo mRNA synthesis by reovirus cores in the presence of S30INT is the same as in the presence of S30C. However, the methylation of the de novo synthesized reo mRNA by the core-associated methylating enzyme(s) in vitro is inhibited by S30INT but not by S30C. The relevance of these phenomena to the inhibition of reovirus replication in interferon-treated cells remains to be established.

Animals↗
PubMed1977

Messenger RNA methylation, translation and degradation in extracts of interferon-treated cells.

Extracts from interferon-treated, not virus infected EAT cells differ in several biochemical characteristics from extracts of untreated cells. Some of these differences are manifested only if the extracts are supplemented with ds RNA and ATP. Thus, in the extracts from interferon-treated cells these supplements activate a protein kinase and an endonuclease activity as well as an inhibitor of the translation of messenger RNA. The effect of the same supplements in extracts of untreated cells is much less pronounced. Other differences between the two types of extracts do not seem to depend on the addition of ds RNA and ATP. These include an impairment of mRNA cap methylation and an inhibition of peptide chain elongation that can be overcome by the addition of tRNA. The treatment of human (HeLa S3) cells with human interferon is manifested in the cell extract similarly to the treatment of EAT cells with mouse interferon. Studies are underway to isolate and characterize the ds RNA activated enzymes and the inhibitors and to establish how the presence of these in extracts from interferon-treated cells can account for the impairment of virus replication by interferon.

Adenosine Triphosphate↗
PubMed1976

Interferon, double-stranded RNA, and protein phosphorylation.

We reported earlier that the addition of double-stranded RNA and ATP increases the endonuclease activity more in an extract of Ehrlich ascites tumor cells which have been treated with an interferon preparation than in a comparable extract from control cells. We report here that the addition of double-stranded RNA to an extract from Ehrlich ascites tumor cells which have been treated with an interferon preparation [or with the interferon inducer poly(I)-poly(C)] promotes the phosphorylation by [gamma-32P]ATP of at least two proteins: P1 (molecular weight of 64,000) and P2 (molecular weight of 37,000). Double-stranded RNA also promotes the phosphorylation of at least one (i.e., P1) of these two proteins in an extract from cells which have not been treated with interferon, but the extent of phosphorylation is much smaller. Double-stranded RNA which has been degraded by RNase III, or DNA, does not promote the phosphorylation.

Adenosine Triphosphate↗