Structure of late adenovirus 2 heterogeneous nuclear RNA

Abstract

Late adenovirus 2 messenger RNAs are processed from a single transcriptional unit some 20,000 nucleotides in length. All of these cytoplasmic RNAs have multiple leaders spliced to their 5′ termini; the most common form is a tripartite leader set. Sequences complementary to the 5′ proximal leader lie adjacent to position 17, the site for initiation on this transcriptional unit. The structure of steady-state nuclear RNA in late adenovirus 2-infected cells has been analyzed both by electron microscopy of hybrids of nuclear RNA and restriction endonuclease cleavage fragments, and digestion of similar hybrids with single-strandspecific nucleases and resolving the protected DNA strands by electrophoresis in agarose gels. While all cytoplasmic mRNAs have three or more leader segments spliced together following excision of appropriate intervening sequences, long nuclear RNA contains some or all of these intervening sequences. Long completely colinear nuclear RNAs have 5′ termini at position 17 on the genome. All other nuclear RNA forms with one or two intervening segments excised have a structure consistent with the proposition that the 5′ proximal splice must occur before the second internal segment of intervening sequences can be excised. Long nuclear viral RNAs typically have unique 3′ termini, which map in the same position as the 3′ termini of cytoplasmic mRNAs. In general, the structure of steady-state nuclear late adenovirus 2 RNA is consistent with these molecules being intermediates in the intramolecular processing of mRNA from a much longer initial transcript.