Assembly of a ribonucleoprotein catalyst by tertiary structure capture.

CBP2 is an RNA tertiary structure binding protein required for efficient splicing of a yeast mitochondrial group I intron. CBP2 must wait for folding of the two RNA domains that make up the catalytic core before it can bind. In a subsequent step, association of the 5' domain of the RNA is stabilized by additional interactions with the protein. Thus, CBP2 functions primarily to capture otherwise transient RNA tertiary structures. This simple one-RNA, one-protein system has revealed how the kinetic pathway of RNA folding can direct the assembly of a specific ribonucleoprotein complex. There are parallels to steps in the formation of a much more complex ribonucleoprotein, the 30S ribosomal subunit.