Overexpression of essential splicing factor ASF/SF2 blocks the temporal shift in adenovirus pre-mRNA splicing and reduces virus progeny formation

Expression of cytoplasmic mRNA from most adenovirus transcription units is subjected to a temporal regulation at the level of alternative pre-mRNA spl icing. The general tendency is that splice site selection changes from prox imal to distal late after infection. Interestingly, ASF/SF2, which is a pro totypical member of the SR family of splicing factors, has the opposite eff ect on splice site selection, inducing an increase in proximal splice site usage. We have previously shown that SR proteins late during an adenovirus infection become partially inactivated as splicing regulatory proteins, A p rediction from these results is that overexpression of an SR protein, such as ASF/SF2, during virus growth will interfere with virus replication by di sturbing the balance of functional and nonfunctional,ASF/SF2 in the infecte d cell. To test this hypothesis, we reconstructed a recombinant adenovirus expressing ASF/SF2 under the transcriptional control of a regulated promote r. The results show that, as predicted, induction of ASF/SF2 during lytic v irus growth prevents the early to late shift in mRNA expression from both e arly (EIA and E1B) and late (L1) transcription units, Furthermore, ASF/SF2 overexpression blocks viral DNA replication and reduces selectively cytopla smic accumulation of major late mRNA, resulting in a lower virus yield. Col lectively, our results provide additional support for the hypothesis that v iral control of SR protein function is important for the proper expression of viral proteins during lytic virus growth.