FIG. 4.

Identification of snRNA cross-linked to pre-mRNA. (A) Splicing reaction mixtures containing m⁷GpppG-capped Ad1WW were irradiated (as shown in Fig. 3, lane 3) and resolved on a 5% preparative polyacrylamide gel. (B) The cross-linked products shown in panel A were digested with RNase H and oligonucleotides complementary to either U1, U2, U5, or U6 snRNA and then fractionated onto a 5% polyacrylamide gel. The diagram above each gel indicates the identity of the snRNA shown to be cross-linked to the pre-mRNA.