[Synthesis and interaction of two peptides, modeling the DNA-binding domain of the v-jun transcription activator, with DNA].

Synthesis and DNA-binding activities of the two synthetic 26-residue peptides, containing in two copies a part of the DNA-binding region of the transcription activator v-Jun, are reported. Aminoacid sequences of the two peptides are identical, but in one of them the structure of the DNA-binding region is stabilized by S-S-bond between the two cysteine residues. Using CD spectroscopy, it is shown that the two peptides exist in a random coil conformation in aqueous solution, but assume partially an alpha-helical conformation in the presence of 20% trifluoroethanol. The percentage of alpha-helix is increased in the presence of 40% trifluoroethanol up to approximately 65% and 40% in the absence and presence of S-S-bond between the two cysteine residues, respectively. Evidently, formation of S-S-bond prevents a coil to alpha-helix transition in one of the two DNA-binding regions of the peptide, whereas the formation of alpha-helix in another DNA-binding region is allowed. It is shown that the two peptides bind to DNA. We found that the DNA minor groove-binding antibiotic distamycin A competes with the two peptides for binding to poly(dA).poly(dT). The binding of the two peptides to DNA is accompanied by conformational transitions in the peptide molecules, whereas the structure of DNA does not undergo a marked change. The difference CD spectrum obtained by subtracting the spectrum of DNA from the spectrum of a peptide-DNA mixture differs from the CD spectrum of the free peptide. The shapes of the difference CD spectra are consistent with alpha-beta and coil-beta transitions induced upon binding of the two peptides to DNA. DNase I footprinting diagrams show that peptides mediated cleavage protection of DNA takes place at regions containing 5'-TGA-3' and 5'-TGC-3' nucleotide sequences.