Ribonucleoprotein and protein factors bind to an H-DNA-forming c-myc DNA element: possible regulators of the c-myc gene.

We have located a positive, cis-acting DNA sequence element within the 5' flanking DNA of the c-myc gene (-125 base pairs). This DNA sequence element has a large purine-pyrimidine strand asymmetry and can assume the H-DNA conformation. A factor with the properties of a ribonucleoprotein (RNP) interacts with this DNA region. The interaction of the c-myc DNA sequence element and the RNP involves an RNase H-sensitive mechanism and, therefore, may involve an RNA.DNA hybrid. In addition, a protein factor(s) binds to this DNA sequence element. DNA footprinting and mutant oligonucleotide binding/competition assays implicate a punctate, poly(G.C) recognition/binding sequence for the RNP factor, whereas the major protein factor requires two ACCCT sequence motifs for maximal binding. These results suggest that RNP and protein factors act as positive transcriptional regulators of the c-myc gene, perhaps by altering DNA topology.