Two adenovirus mRNAs have a common 5' terminal leader sequence encoded at least 10 kb upstream from their main coding regions.

The messenger RNAs encoding two late adenovirus serotype 2 (Ad2) proteins, fiber and 100K, were purified by hybridization to restriction endonuclease fragments of Ad2 DNA followed by electrophoresis on polyacrylamide gels containing 98% formamide. The 5' terminal oligonucleotides generated by RNAase T1 digestion of the messengers were selected by dihydroxyboryl-cellulose chromatography. Both mRNAs gave an identical 5'-undecanucleotide with the general structure 7mG5'ppp5'AmC(m)U(C4,U3)G. This undecanucleotide could be removed by mild RNAase treatment from the mRNA after hybridization to DNA fragments containing the main coding sequence of the messenger. In contrast, a small region defined by Bal I-E (14.7-21) protects this undecanucleotide from RNase. A second region contained within both Hind III-B (17-31.5) and Hpa I-F (25.5-27.9), although unable to protect the undecanucleotide, hybridizes to both fiber and 100K mRNAs and protects a similar sequence of 100-150 nucleotides. These observations suggest that both mRNAs contain a long common sequence, complementary to at least two different sites on the Ad2 genome remote from the start of these two genes. The implications of these findings are discussed, and a general mechanism is presented for the biosynthesis of mRNAs from larger precursor molecules, based on intramolecular ligation.