Expression of defective-interfering influenza virus-specific transcripts and polypeptides in infected cells

We have previously shown that influenza virus defective-interfering particle (DI) RNAs can be transcribed into polyadenylated complementary RNAs in vitro (Chanda et al., J. Virol. 45:55-61, 1983). In this paper we report that influenza virus DI RNAs can be transcribed into mRNAs in infected cells as well. The DI-specific RNAs (both plus and minus strands) were found to be synthesized in molar excess compared with RNAs of standard virus segments. In addition, two DI preparations (DI3 and DI7) produced novel polypeptides not present in standard virus-infected cells. These novel polypeptides in DI-infected cells were of PB2 origin, as were the major DI RNA species in both DI preparations. Furthermore, these polypeptides were shown to arise from the translation of functional mRNAs transcribed from DI3 and DI7 RNAs and not from either the degradation of PB2 protein or the incomplete translation of PB2 mRNA. Using mixed-infection tests with different DI preparations, we found that the ability of DI to produce detectable novel polypeptides does not necessarily confer any replicative or interfering advantage over other DI which do not produce detectable DI-specific polypeptides. The possible role of DI-specific polypeptides in DI-mediated interference is discussed.