ALTERNATE SPLICING CREATES 2 FORMS OF THE HUMAN KIT PROTEIN

The Kit gene encodes for a transmembrane tyrosine kinase receptor that is expressed during early hematopoiesis and in a large proportion of blast cells of patients with acute myeloblastic leukemia (AML). Tissue culture studies have revealed that the growth factor recognized by th e Kit protein is a stimulator of both colony formation and self renewa l of AML cells. During an analysis of the Kit gene in AML cells we ide ntified two different RNA transcripts differing by 12 nucleotides just 5' of the transmembrane encoding region. Analysis of a variety of tis sues revealed that both forms of RNA are expressed in all of the tissu es that produce Kit. Sequencing of the corresponding genomic region re vealed that the two forms of RNA arose through the alternate use of 5' splice donor sites.