CRY2olig corresponds to the N-terminal photolyase homology region (PHR) of the Arabidopsis thaliana CRY2 gene (TAIR:28374), with an E490G amino acid substitution. When exposed to blue light, CRY2olig undergoes rapid, reversible, and robust oligomerization within seconds (the E490G mutation greatly enhances this light-inducible clustering compared to that seen with the wild-type PHR region). This property can be used to study protein interaction dynamics in vivo, and can also be used to transiently and reversibly control protein function in a light-dependent manner (adapted from PMID:25233328).