CHARACTERIZATION OF A MAX-DNA COMPLEX BY CROSS-LINKING TO PHOTOACTIVEOLIGONUCLEOTIDES

The structure of the Max:DNA complex was investigated by cross-linking Max to a series of photoactive oligonucleotides. A single photoactive aryl azide was introduced into oligonucleotides at defined positions downstream from the specific CACGTG binding site. Purified Max homodim ers bound to and were cross-linked to oligonucleotides containing a ph otoactive group either 2,5,8, or 11 bp downstream from the binding sit e. Further analysis revealed that an amino-terminal chymotryptic pepti de of Max was cross-linked to the oligonucleotide containing a photoac tive probe 11 bp downstream from the specific binding site. This resul t is consistent with the recent crystal structure of the Max:DNA compl ex (Ferre-D'Amare et al., 1993) and further suggests that amino acid r esidues near the amino-terminus of Max are in close proximity to a reg ion of DNA that is separated from the core binding site by one turn of the double helix.