Organization and analysis of the promoter region and 5' non-coding exons of the human c-src proto-oncogene.

In order to help clarify the cellular mechanisms that regulate expression of the human c-src proto-oncogene, we have isolated a series of overlapping genomic clones that contain the c-src promoter region, as well as three previously uncharacterized exons. These exons encode the 350-bp 5' untranslated region of the c-src mRNA and span 35 kb of genomic DNA, extending the human c-src locus to approximately 60 kb. Subcloning and sequence analysis of the 5' flanking region of the gene revealed a high GC content and several consensus Sp1 and AP2 binding sites. However, TATA or CAAT boxes were not present, a characteristic shared by other GC-rich promoters. Promoter-CAT constructs demonstrated that the promoter was functional in transfection assays and that its activity was dependent on correct orientation. CAT-promoter deletion constructs were used to define the 5' boundary for maximal promoter activity and to reveal the presence of both positive and negative regulatory elements. S1 analyses of human c-src mRNA from cell lines indicated that multiple transcription start sites were utilized.