DNA template effect on RNA splicing: two copies of the same gene in the same nucleus are processed differently.

Many cellular and viral genes are parts of complex transcription units containing multiple splicing choices. During the course of an adenoviral replicative cycle, different spliced versions of a single gene predominate, depending on the stage of infection. This is true for several adenoviral genes. In this paper we show for the viral E1B transcription unit that splice site usage regulates this process. The change in alternative splicing in this system does not depend on the sequence of the transcribed genes. Non-adenoviral genes, such as the SV40 early region and the polyoma early region, which normally show little or no regulation of spliced RNA product formation, become regulated for mRNA production after insertion into the adenoviral genome. Additional studies show that E1B splicing regulation in adenovirus is a cis effect. Staggered infections using two discernable viral genomes resulted in a situation where both early and late genomes exist in the same nucleus. Neither genome was able to impose its regulated splicing pattern on the other, indicating that the cue for the switch in viral gene splicing is not directly dependent on global changes in trans-acting splicing factors. This suggests a model where the signal for changes in RNA processing for the E1B gene is linked to the state of the DNA template or its localization within nuclear subcompartments.