Knowledge of the three-dimensional structure of the bacteriophage λ Cro repressor, combined with an analysis of amino acid sequences and DNA coding sequences for this and other proteins that recognize and bind specific base sequences of double-helical DNA, suggests that a portion of the structure of the Cro repressor that is involved in DNA binding also occurs in the Cro protein from bacteriophage 434, the cII protein from bacteriophage λ, the Salmonella phage P22 c2 repressor and the cI repressor from bacteriophage λ. This α-helical super-secondary structure may be a common structural motif in proteins that bind double-helical DNA in a base sequence-specific manner.
Bibliographical noteFunding Information:
for Nucleic Acid Interactions. We thank D. Bacon and Dr S. J. Remington for computer programs, D. Knudsen for running computer programs, Dr A. Taylor for assistance with the DNA sequence comparisons, and Drs M. N. G. James and M. Rosenberg for helpful discussions. This work was supported by the Canadian Medical Research Council Group on Protein Structure and Function and grants from the National Science Foundation (PCM-m 8014311) and National Institutes of Health (GM 26066; GM 28138). One author (D.H.O.) was supported by the Damon Runyon-Walter Winchell Cancer Fund Postdoctoral Fellowship (DRG&303-F).