Required for the splicing of group IIB introns in chloroplasts. Forms complexes with either CAF1 or CAF2 which, in turn, interact with RNA and confer intron specificity of the splicing particles. Has no peptidyl-tRNA hydrolase activity. Interacts with CAF1 and CAF2. Part of large ribonucleo-protein complexes that include group IIB introns and either CAF1 or CAF2. Belongs to the PTH family. CRS2 subfamily.