RNase protection analysis showed multiple transcriptional initiation sites. Two major and one minor protected bands, indicating the transcriptional start sites, were detected in the WB and H510 SCLC cell lines as well as the HEL leukemia cell line. These respectively correspond to base +1 (41 bp from 3′ BamHI site), +3, and +7 in Fig 2. The upper major band comigrated with a 41-base RNA size marker made by transcribing BamHI-cut pGEM3 with SP6 polymerase.