Production of a truncated human c‐myc protein which binds to DNA

Abstract

Two kinds of truncated human c‐myc proteins were produced in Escherichia coli. The human c‐myc gene is composed of three exons, exons 2 and 3 having coding capacity for a protein of 439 amino acids. 252 N‐terminal amino acids are encoded by exon 2, the C‐terminal 187 amino acids being encoded by exon 3. One of the proteins (p42) produced in E. coli corresponds to 342 amino acids from the 98th Gln to the C‐terminus, plus 21 amino acids derived from the H‐ras gene at the N‐terminus. The other (p23) corresponds to 155 amino acids from the 98th Gln to the 252nd Ser, plus five amino acids (Gly‐Gly‐Thr‐Arg‐Arg) at the C‐terminus, plus 21 amino acids from the H‐ras gene at the N‐terminus. The p23 protein was produced by using cDNA in which a frame shift occurred at the boundary between exons 2 and 3. We investigated the DNA‐binding activity in p42 and p23 proteins. DNA‐cellulose column chromatography showed that p42 binds to DNA, whereas p23 does not. This DNA‐binding activity of p42 was inhibited by antiserum prepared against p42 but not by antiserum against p23. This indicates that the DNA‐binding activity of c‐myc protein is localized in the portion encoded by exon 3.