Sequences of Fas gene cDNA clones derived from Fas-negative ATL cells. Sequences of Fas gene cDNA from Fas-negative ATL cells were determined as described in the Materials and Methods. In the clones sequenced, four clones lacked exon 4 (A). The other five clones showed a 5-bp deletion and a 1-bp insertion in exon 2 (B). Both mutations caused premature termination of Fas gene translation.