The c-myc gene comprises three exons with a single
large AUG-initiated open reading ‘frame extending
from exon 2 through exon 3. Exon 1 lacks any AUG
codons. Cells from a wide range of species produce
two c-myc proteins that, while highly related, do not
appear to arise from posttranslational interconver-
sion. To understand the origin of the two proteins, we
mapped them and analyzed the in vitro protein-coding
capacity of c-myc cDNAs. Our findings show that the
two proteins are derived from alternative translational
initiations at the exon 2 AUG and at a non-AUG codon
near the 3’ end of exon 1, resutting in the production
of proteins with distinct N termfni. In Burkitt’s lympho-
mas, the removal or specific mutation of exon 1 in
c-myc translocations correlates with suppression of
synthesis of the larger protein, and thus may contrib-
ute to the oncogenic activation of c-myc.