Splicing of adenovirus RNA in a cell-free transcription system.

A soluble whole-cell extract prepared accurately from HeLa cells splices 2-3% of the RNA transcribed from a DNA template containing the first and second leader exons of late adenovirus RNA. The spliced RNA was detected by a sensitive technique using hybridization to a single-stranded phage M13 cDNA clone, followed by binding to nitrocellulose filters. The identity of the spliced RNA was established by RNase T1 and pancreatic RNase two-dimensional peptide mapping. The bond formed during the in vitro splicing reaction appears to be a typical 3',5'-phosphodiester bond as judged by its sensitivity to RNase T1. The splicing reaction is specifically inhibited by KCl at concentrations greater than 50 mM and by the addition of cellular RNA. Three features of this system may account for the detection of splicing in a soluble extract: (i) the sensitive and unambiguous hybridization assay, (ii) the high transcriptional activity of the major late promoter of adenovirus, and (iii) the use of the first and second leader exon splice of adenovirus, which may be unusually rapid.