STABLE, MONOMERIC VARIANTS OF LAMBDA-CRO OBTAINED BY INSERTION OF A DESIGNED BETA-HAIRPIN SEQUENCE

λ Cro is a dimeric DNA binding protein. Random mutagenesis and a selection for Cro activity have been used to identify the contacts between Cro subunits that are crucial for maintenance of a stably folded structure. To obtain equivalent contacts in a monomeric system, a Cro variant was designed and constructed in which the antiparallel β-ribbon that forms the dimer interface was replaced by a β-hairpin. The engineered monomer has a folded structure similar to wild type, is significantly more stable than wild type, and exhibits novel half-operator binding activity.