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Summary The plant alkaloid camptothecin inhibits interferon production induced by Newcastle disease virus (NDV) or ultraviolet-irradiated NDV in chick and human cells, and by Sindbis virus in chick cells. It has no effect on interferon production induced by poly(rI).poly(rC) in chick and human cells. No effect of camptothecin could be detected on the multiplication of NDV, and it is concluded that the inhibition reflects a difference between interferon induction by viruses and by polynucleotides.

Summary Messenger RNA (mRNA) with sequences of polyriboadenylic acid (poly A) has been isolated from the cytoplasm of vaccinia virus-infected cells after a short pulse label with radioactive uridine. No labelled RNA containing poly A was isolated from mock-infected cells under the same conditions. mRNA synthesized at various times during the replicative cycle was examined by polyacrylamide gel electrophoresis and compared with the mRNA synthesized in the presence of inhibitors of protein and DNA synthesis. No difference was detected between ‘class 1’ and ‘class 2 early’ mRNA species although ‘late’ RNA species were on average considerably larger than the ‘early’ species.