Groups of adenovirus type 2 mRNA's derived from a large primary transcript: probable nuclear origin and possible...

Late in adenovirus type 2 infection, a number of mRNA's apparently arise by processing a large nuclear transcript that represents the right-hand 85% of the genome (summarized in Evans et al., Cell 12:733-739, 1977). Hybridization of labeled late mRNA to a series of DNA restriction fragments representing the right-hand 70% of the genome demonstrates at least 12 discrete mRNA's that appear to fall into five groups, each possibly containing a common 3' terminus. The processing necessary to generate these mRNA's apparently occurs in the nucleus. All the mRNA's appear to contain a sequence of approximately 100 nucleotides complementary to a fragment with coordinates 25.5-27.9. This fragment contains one of the regions found by Berget et al. (Proc. Natl. Sci. U.S.A. 74:3171-3175, 1977), Chow et al. (Cell 12:1-18, 1977), and Klessig (Cell 12:9-22, 1977) to the "spliced" onto the 5' end of late adenovirus type 2 mRNA's. Because the sequences to be spliced exist only once per large transcript, any of the mRNA-specific regions might only be preserved from a small fraction of the transcripts. Measurement of the transport efficiency of regions of the large nuclear transcript, if fact, shows that only 15 to 25% of any particular region is transported to the cytoplasm. The overall conclusion of these experiments is that the large late nuclear transcript can be processed in the nucleus to yield any one of many (approximately 12) mRNA's; the unused portions of the primary transcript then accumulate in the nucleus or are destroyed.