SYNTHESIS AND BINDING TO DNA OF 2 PEPTIDES MODELING THE DNA-BINDING DOMAIN OF TRANSCRIPTION ACTIVATOR V-JUN

Synthesis and interaction with DNA of two 26-residue peptides, each containing in two copies a fragment of the DNA-binding domain of the transcription activator v-Jun, are described. The peptides have identical amino acid sequence but one is stabilized by an S-S bond between two cysteine residues. CD spectroscopy showed that both peptides have a random conformation in an aqueous solution, and assume a partly alpha-helical conformation in the presence of 20% trifluoroethanol. The relative content of alpha-helix increases in the presence of 40% trifluoroethanol to approximately 66% and 40%, respectively in the absence and in the presence of the S-S bond. Obviously the S-S bond hinders the formation of alpha-helix within one of the DNA-binding regions of the peptide, though an alpha-helix can probably be generated in the other part. Both peptides were shown to bind to DNA. We revealed that the DNA minor groove-binding antibiotic distamycin A competes effectively with the peptide for binding to poly(dA).poly(dT). Binding of the peptide to DNA induces a conformational transition in the peptide molecule, while the DNA structure does not appreciably change. The difference CD spectra obtained by subtracting the spectrum of free DNA from that of a peptide-DNA mixture differs from the spectrum of the free peptide. The shapes of the difference spectra are consistent with alpha --> beta and coil --> beta transitions induced upon binding of the peptides to DNA. DNase I footprinting diagrams show that the peptides protect the DNA from cleavage at the regions containing 5'-TGA-3' and 5'-TGC-3' sequences.