Expression of FasLs and FasL mRNA in 3DO cells. RNase protection analysis was performed as described in Materials and Methods. Probe includes a portion of exon 1 and a portion of exon 4. On the left, the fragment that the antisense probe would protect upon single-strand specific RNase digestion is shown schematically. Line 1, undigested probe; line 2, probe digested after hybridization with 30 μg tRNA; line 3, probe digested after hybridization with 30 μg RNA from 3DO cells; line 4, probe digested after hybridization with 30 μg RNA from anti-CD3–stimulated 3DO cells. The basepair length reported on the right was derived from a sequencing reaction.