Early capping of transcripts from the adenovirus major late transcription unit.

The various events which result in modification of a primary RNA transcipt may have a role in choosing transcripts which are to be processed into mRNA. If there is a stepwise and interdependent nature to each of the modifications then it is important to place the various steps in temporal order. We show here that the formation of a capped 5' terminus seems to be a very early event for adenovirus type 2 (Ad-2) nuclear RNA that is initiated at the major late Ad-2 promoter. There is an equally rapid entry of 3H-adenosine into the cap and the first dozen or so adenylate residues in the RNA chain. Taken together with evidence on general mRNA metabolism in Chinese hamster cells, it seems unlikely that capping has any differential role in successful RNA processing rather is an automatic event for all RNA polymerase II products.