Analyses of the synthesis of virus-specific RNA in fowl plague virus-infected chick embryo cells are reported. The genome of this strain of influenza virus appears to consist of 10 single-stranded RNAs with molecular weights ranging from approximately 105 to 106. The synthesis of both virion RNA and complementary RNA occurs mainly at early times during infection. The complementary RNAs are of two types which are distinguished by a number of properties, and each population, which is made up of molecules complementary to all 10 genome RNAs, clearly serves a different function. The polyadenylated cRNAs which appear to be incomplete transcripts of each genome RNA molecule are exclusively associated with polysomes and therefore comprise the virus mRNA. The synthesis of these molecules is controlled throughout infection with respect to both the amount of each transcript produced and the time at which it is produced in maximum amount. The unpolyadenylated cRNAs on the other hand are complete transcripts of each genome RNA and are produced in similar relative amounts during 3 hr of infection; it is suggested that these molecules serve as template for replicating the virus genome. It is also apparent from these investigations that the two types of cRNA are synthesised by the same transcriptase but that the production of unpolyadenylated complete transcripts is dependent upon the synthesis of certain other viral protein(s).
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