No abstract

We have identified a positive modulator within the c‐myc first exon downstream of the gene's transcription initiation sites, P1 and P2. We introduced myc‐CAT (chloramphenicol acetyltransferase) hybrid genes into three cell lines (BJAB, COS and HeLa) and measured their expression by either CAT enzymatic activity, S1 nuclease protection or by a nuclear ‘run‐on’ transcription assay. Removal of 46 bp from the 3′ end of the first exon results in a decrease of myc‐CAT expression and P2 activity. A 438‐bp exon 1 segment, lacking the normal myc promoters, efficiently drives the expression of SV40 early promoters. We find that this first exon segment efficiently functions as a positive modulator only in its sense orientation, 3′ of a nearby promoter. The positive effects of the myc first exon and the SV40 enhancer are complementary.

A block to elongation of transcription has been shown to occur within the first exon of the human and murine c-myc genes.

No abstract