Selective targeting of sequences in bcr/abl mRNA for in vitro degradation by RNase L activated with 2-5A–antisense. (A) Construction of plasmids for in vitro synthesis of bcr/abl and 5′-bcr RNA segments (Materials and Methods). (B) The positions of the 5′-bcr and b3/a2 fusion site RNAs are indicated in the autoradiogram of the dried, SDS/polyacrylamide gel (arrows). Lane 1, absense of ODN; lanes 2 to 4: 50, 100, and 200 nmol/L of SpA₄-anti-b3a2; lanes 5 to 7: 50, 100, and 200 nmol/L of SpA₄-antibcr. The b3a2 RNA was labeled to a higher specific activity than the 5′ bcr segment, and thus appears darker in the autoradiogram, although equivalent amounts were included.