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 repo 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)J promotes the phosphorylation by Tris-CI at pH 7.6, 80 mM KCI, 4 mM MgCl2, and 6 mM 2-mercaptoethanol, the S30INT.s and S30c.s extracts were produced. S30 extracts from EAT cells treated with the interferon-inducer poly(I)-poly(C) (1) were prepared according to published procedures (11). The yield of vesicular stomatitis virus from infected cells in a single growth cycle was reduced by over 95% in cells treated with interferon, and by over 99% in those treated with poly(I)-poly(C). S30 extracts from EAT cells were

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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 Ehrlich ascites tumor cells (S30INT). We find now that after the methylation of reo mRNAu has stopped in S301NT, the RNA can be reisolated and further methylated in an extract of control cells (S30C). Thus the impairment of methylation in S301NT cannot be due to cleavage or irreversible inactivation of reo mRNAu. Freshly added reo mRNAu can be methylated in S301NT in which the methylation of previously added reo mRNAu has stopped. This indicates that the impairment is not due to the depletion ofS-adenosylmethionine (the methyl donor), the accumulation of S-adenosylhomocysteine (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 S301NT

SUMMARYExtracts from mouse interferon-treated mouse cells (Ehrlich ascites tumour and L929) were reported earlier to differ in several characteristics from extracts of untreated ceils. We report now that the effect of treatment with human interferon of cells of a human line (HeLa $3) is similarly manifested in the cell extract. A comparison of extracts from interferon-treated HeLa $3 cells (S3o~r) with that from untreated cells ($3oc) revealed: (a) an impairment in S3OrNT of the methylation of (unmethylated) reovirus mRNAs by the cellular and virus enzymes; (b) a faster degradation of reovirus mRNAs in S3o~T but only in reaction mixtures supplemented with double-stranded RNA and ATP ;(c) an increased phosphorylation by ATP of one (or two), proteins in S3Or~T but only in reaction mixtures supplemented with double-stranded RNA and (d) a more pronounced inhibition of translation by double-stranded RNA in S3o~T. No such effects were observed in extracts prepared from HeLa cells treated with mouse interferon.