title: Group II intron splicing factors derived by diversification of an ancient RNA-binding domain.
abstract: Group II introns are ribozymes whose catalytic mechanism closely resembles that of the spliceosome. Many group II introns have lost the ability to splice autonomously as the result of an evolutionary process in which the loss of self-splicing activity was compensated by the recruitment of host-encoded protein cofactors. Genetic screens previously identified CRS1 and CRS2 as host-encoded proteins required for the splicing of group II introns in maize chloroplasts. Here, we describe two additional host-encoded group II intron splicing factors, CRS2-associated factors 1 and 2 (CAF1 and CAF2). We show that CRS2 functions in the context of intron ribonucleoprotein particles that include either CAF1 or CAF2, and that CRS2-CAF1 and CRS2-CAF2 complexes have distinct intron specificities. CAF1, CAF2 and the previously described group II intron splicing factor CRS1 are characterized by similar repeated domains, which we name here the CRM (chloroplast RNA splicing and ribosome maturation) domains. We propose that the CRM domain is an ancient RNA-binding module that has diversified to mediate specific interactions with various highly structured RNAs.
authors.affiliation: Institute of Molecular Biology, Department of Chemistry, University of Oregon, Eugene, OR 97403, USA.
authors.forename: Gerard J
authors.initials: GJ
authors.lastname: Ostheimer
authors.forename: Rosalind
authors.initials: R
authors.lastname: Williams-Carrier
authors.forename: Susan
authors.initials: S
authors.lastname: Belcher
authors.forename: Erin
authors.initials: E
authors.lastname: Osborne
authors.forename: Jennifer
authors.initials: J
authors.lastname: Gierke
authors.forename: Alice
authors.initials: A
authors.lastname: Barkan
mesh_terms: D000595:Amino Acid Sequence; D001483:Base Sequence; D002736:Chloroplasts / Q000235:genetics; D017931:DNA Primers; D007438:Introns; D008969:Molecular Sequence Data; D009687:Nuclear Proteins / Q000737:chemistry / Q000378:metabolism; D010940:Plant Proteins / Q000737:chemistry / Q000378:metabolism; D011233:Precipitin Tests; D012326:RNA Splicing; D000072260:RNA Splicing Factors; D016601:RNA-Binding Proteins / Q000737:chemistry / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid; D020798:Two-Hybrid System Techniques; D003313:Zea mays / Q000235:genetics
chemical_list: C436683:CRS1 protein, Zea mays; D017931:DNA Primers; D009687:Nuclear Proteins; D010940:Plant Proteins; D000072260:RNA Splicing Factors; D016601:RNA-Binding Proteins