CRS1 is a novel group II intron splicing factor that was derived from a domain of ancient origin

a1 Institute of Molecular Biology, University of Oregon, Eugene, Oregon 97403, USA


Protein-dependent group II intron splicing provides a forum for exploring the roles of proteins in facilitating RNA-catalyzed reactions. The maize nuclear gene crs1 is required for the splicing of the group II intron in the chloroplast atpF gene. Here we report the molecular cloning of the crs1 gene and an initial biochemical characterization of its gene product. Several observations support the notion that CRS1 is a bona fide group II intron splicing factor. First, CRS1 is found in a ribonucleoprotein complex in the chloroplast, and cofractionation data provide evidence that this complex includes atpF intron RNA. Second, CRS1 is highly basic and includes a repeated domain with features suggestive of a novel RNA-binding domain. This domain is related to a conserved free-standing open reading frame of unknown function found in both the eubacteria and archaea. crs1 is the founding member of a gene family in plants that was derived by duplication and divergence of this primitive gene. In addition to its previously established role in atpF intron splicing, new genetic data implicate crs1 in chloroplast translation. The chloroplast splicing and translation functions of crs1 may be mediated by the distinct protein products of two crs1 mRNA forms that result from alternative splicing of the crs1 pre-mRNA.

(Received March 28 2001)
(Revised April 19 2001)
(Accepted May 25 2001)

Key Words: chloroplast; maize; plastid; RNA chaperone.

c1 Reprint requests to: Alice Barkan, Institute of Molecular Biology, University of Oregon, Eugene, Oregon 97403, USA; e-mail: abarkan@molbio.uoregon.edu.
p1 Present address: Fred Hutchinson Cancer Research Center, 1100 Fairview Avenue North, Seattle, Washington 98109-1024, USA.
p2 Present address: Botanisches Institut, Ludwig Maximilians Universitaet Muenchen, Menzinger Str. 67, 80683 Muenchen, Germany.