Genetics, Vol 130, 17-26, Copyright © 1992

INVESTIGATIONS

Mutant {lambda} Repressors With Increased Operator Affinities Reveal New, Specific Protein-DNA Contacts

N. Benson, C. Adams and P. Youderian
Present address: Department of Biology, University of Utah, Salt Lake City, Utah 84112.

The binding specificities of four mutant {lambda} cl repressor proteins with increased affinities for operator DNA were examined. Two mutant repressors (Glu(34) -> Lys and Glu(83) -> Lys) have the same specificity of binding as wild-type repressor, whereas two (Gly(48) -> Ser and Gly(48) -> Asn) have new binding specificities. The Gly(48) -> Asn mutant repressor recognizes {lambda} operators with changes at base pair 3 with a different order of affinity than wild-type repressor, suggesting that the side chain of Asn(48) makes additional specific DNA contacts at or near this base pair. When paired with a change that disrupts the specific interaction of the amino-terminal arm of {lambda} repressor with DNA (Lys(4) -> Gln), one change that increases the affinity of repressor (Gly(48) -> Ser) suppresses the binding defect of the Lys(4) -> Gln repressor, resulting in a double mutant repressor with a new binding specificity different than that of both its parents and of wild type. These results lend strong support to the model of direct recognition of the {lambda} operator by {lambda} repressor proposed from the crystal structure of the repressor/operator complex.

This article has been cited by other articles:

				S E Wells, M Neville, M Haynes, J Wang, H Igel, and M Ares CUS1, a suppressor of cold-sensitive U2 snRNA mutations, is a novel yeast splicing factor homologous to human SAP 145. Genes & Dev., January 15, 1996; 10(2): 220 - 232. [Abstract] [PDF]