RNase protection assay of Fas gene transcripts. The reaction mixtures were digested with ribonuclease and electrophoresed in a 2.5% agarose gel. In normal PBMCs, the intact and spliced Fas gene transcripts (small arrowheads) were detected (lane 1). In cases no. 4 and 5 (lanes 2 and 3, respectively), additional bands (big arrowheads) could be found. In the Fas-negative ATL case, multiple bands were identified (lane 4, case no. 2), two of which corresponded to bands in case no. 4.