2-STAGE THERMAL UNFOLDING OF [CYS55]-SUBSTITUTED CRO REPRESSOR OF BACTERIOPHAGE-LAMBDA

It has been shown by scanning calorimetry and H-1 NMR spectroscopy that thermal denaturation of mutant lambda-phage cro repressor in which Val55 was substituted for Cys, proceeds in 2 stages in contrast to the wild type protein. At neutral pH values, an additional cooperative transition has been observed at about 100-degrees-C. Calorimetric measurements on the mutant and its tryptic fragment lead to the conclusion that the two-stage character of thermal unfolding of the mutant is due to a disruption of an additional cooperative domain in the dimer molecule which is stabilized by the S-S crosslink.