Application of an exonuclease assay developed in this laboratory to identify and map the sites of tight protein-DNA interactions on large pieces of DNA, to the c-myc gene has revealed multiple cis- and trans-elements both upstream and downstream of the c-myc promoter P1. We have focused on 4 regions, each of which interacts with one or more sequence-specific binding proteins. 1 .300 bp upstream of P1, fos/jun (APl) and octamer binding proteins bind to a common negative element. 2.Approximately 1 kb downstream, a 140 kD phosphoprotein binds to a negative element. 3.1.5 kb upstream of P1, a cell-type and differentiation specific 75 kD protein containing peptides, binds to a positive element. 4.100 to 150 bp upstream of P1, a complex set of factors bind to a cytidine-rich element shown to be a positive acting cis-element. Two factors binding to this positive element have been purified in this laboratory. A 60 kD polypeptide as well as a 32 kD species have been shown to interact independently with this c-myc element. Partial protein sequence has been obtained for each factor.
