Early capping of transcripts from the adenovirus major late transcription unit

Abstract

The various events which result in modification of a primary RNA transcript 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^1–5. 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 cells⁶, it seems unlikely that capping has any differential role in successful RNA processing but rather is an automatic event for all RNA polymerase II products.