DNA MOBILITY IN CRYSTALS OF A NONSPECIFIC LAMBDA-CRO DNA COMPLEX/

DNA location in the crystal of the nonspecific lambda crol(GT)(4) .(AC )(4) complex has been studied by the isomorphous replacement method us ing iodinated and brominated oligonucleotides. The results of the sear ch for heavy atom positions combined with previously obtained molecula r replacement data suggest that the DNA octamer occupies two overlappi ng positions, each of the two duplexes (GTGTGTGT).(ACACACAC) belonging to the same imaginary longer double helix and differing only in the s hift by two base pairs along the common sugar-phosphate backbone. In t he crystals of the heavy atom derivatives different orientations of th e DNA octamer are observed as well. It seems reasonable that the DNA m obility of both kinds might be a common feature of crystals of nonspec ific repressor/DNA complexes.