FIG. 4.

Fluorogram of an agarose-urea gel of actinomycin D-resistant mRNAs synthesized in BHK-21 cells infected with recombinant VSV viruses that contained an additional transcriptional unit inserted at the leader-N gene junction. RNAs were labeled, harvested, purified, annealed with oligo(dT), and exposed to RNase H as described in Materials and Methods. The VSV N, P, M, G, and L mRNAs are identified. The inserted mRNA (which varied in size) is indicated by a bracket (see text for details). Recombinant viruses were named according to the number of nucleotides inserted at the leader-N gene junction (indicated above the lanes).