The primary self-assembly reaction of bacteriophage lambda cI repressor dimers is to octamer.

Cooperative binding of the bacteriopbage λ cI repressor dimer to specific sites of the phage operators O R and O L controls the developmental state of the phage. It has long been believed that cooperativity is mediated by self-assembly of repressor dimers to form tetramers which can then bind simultaneously to adjacent operator sites. As a first step in defining the individual energy contributions to binding cooperativity, sedimentation equilibrium and steady-state fluorescence anisotropy methods have been used to study the higher order assembly reactions of the free repressor in solution