In vivo splicing of the premRNAs from early region 3 of adenovirus-2: the products of cleavage at the 5' splice site of the common intron.

The nuclear transcripts of the early region 3 from adenovirus-2 were studied for the presence of the cleavage products of premRNA at the 5' splice site of the first intervening sequence. Two molecules, free exon 1 and intron-exon 2-poly(A) were characterized by complementary methods including Northern blotting, RNase and S1 nuclease mapping, hybrid-selection and primer extension. The intron of the intron-exon 2 molecule is at least partially in a lariat form. A study of the time course of appearance of the 2 molecules shows that their formation occurs after the synthesis of premRNA, the lag period being no more than 1-2 min and before the formation of mature mRNA which starts accumulating after 3-4 min. These data are compatible with the idea that the 5' cleavage products are splicing intermediates in vivo.