Interactions of the 26-39 fragment of the cro protein from lambda bacteriophage with nucleic acids.

A tetradecapeptide with a sequence identical to residues 26-39 of the cro protein from bacteriophage lambda has been synthesized. This peptide has no secondary structure in an aqueous buffer but adopts an alpha-helical conformation in the presence of 20% hexafluoroisopropanol. The fluorescence of the single tyrosyl residue of the cro protein fragment is quenched upon binding to nucleic acids. Proton magnetic resonance has been used to investigate complex formation of the cro protein fragment with a self-complementary decadeoxynucleotide d(AATTGCAATT). Changes in resonance positions and linewidths have been observed for both partners in the 4 complexes which are obtained when either the single-stranded or double-stranded oligonucleotide is mixed with either the random coil or the alpha-helical peptide. These studies are presently extended to the specific complex formed by the cro protein fragment with the OR3 operator sequence.