Characterization of the vav promoter. (A) RNase protection analysis showing major and minor clusters of transcriptional initiation sites for the vav gene in lymphoid (EL-4, W408, and ABLS-8), erythroid (F4N), monocytic (RAW309 and J774), and early myeloid (416B and FDC-P1) cells. No transcripts were detected in NIH3T3 fibroblasts. The length of each protected fragment, numbered from the ATG translation start, was determined from a sequencing reaction run in parallel (not shown). The undigested probe was 356 bp in length.