Dramatically reduced spliceosome in Cyanidioschyzon merolae.
The human spliceosome is a large ribonucleoprotein complex that catalyzes pre-mRNA splicing. It consists of five snRNAs and more than 200 proteins. Because of this complexity, much work has focused on the Saccharomyces cerevisiae spliceosome, viewed as a highly simplified system with fewer than half as many splicing factors as humans. Nevertheless, it has been difficult to ascribe a mechanistic function to individual splicing factors or even to discern which are critical for catalyzing the splicing reaction. We have identified and characterized the splicing machinery from the red alga Cyanidioschyzon merolae, which has been reported to harbor only 26 intron-containing genes. The U2, U4, U5, and U6 snRNAs contain expected conserved sequences and have the ability to adopt secondary structures and form intermolecular base-pairing interactions, as in other organisms. C. merolae has a highly reduced set of 43 identifiable core splicing proteins, compared with ∼90 in budding yeast and ∼140 in humans. Strikingly, we have been unable to find a U1 snRNA candidate or any predicted U1-associated proteins, suggesting that splicing in C. merolae may occur without the U1 small nuclear ribonucleoprotein particle. In addition, based on mapping the identified proteins onto the known splicing cycle, we propose that there is far less compositional variability during splicing in C. merolae than in other organisms. The observed reduction in splicing factors is consistent with the elimination of spliceosomal components that play a peripheral or modulatory role in splicing, presumably retaining those with a more central role in organization and catalysis.
Department of Chemistry, University of Northern British Columbia, Prince George, BC, V2N 4Z9 Canada; and.
Martha R
MR
Stark
Departments of Biochemistry and Molecular Biology, and.
Elizabeth A
EA
Dunn
Department of Chemistry, University of Northern British Columbia, Prince George, BC, V2N 4Z9 Canada; and.
William S C
WS
Dunn
Botany, University of British Columbia, Vancouver, BC, V6T 1Z4 Canada.
Cameron J
CJ
Grisdale
Department of Chemistry, University of Northern British Columbia, Prince George, BC, V2N 4Z9 Canada; and.
Anthony R
AR
Daniele
Department of Chemistry, University of Northern British Columbia, Prince George, BC, V2N 4Z9 Canada; and.
Matthew R G
MR
Halstead
Botany, University of British Columbia, Vancouver, BC, V6T 1Z4 Canada.
Naomi M
NM
Fast
Department of Chemistry, University of Northern British Columbia, Prince George, BC, V2N 4Z9 Canada; and Departments of Biochemistry and Molecular Biology, and rader@unbc.ca.
Stephen D
http://orcid.org/0000-0001-7242-1785
SD
Rader
D020418:Algal Proteins / Q000235:genetics / Q000378:metabolism; D020029:Base Pairing / Q000235:genetics; D006801:Humans; D047468:Immunoprecipitation; D007438:Introns / Q000235:genetics; D008954:Models, Biological; D009690:Nucleic Acid Conformation; D012322:RNA Precursors / Q000235:genetics / Q000378:metabolism; D012326:RNA Splicing / Q000235:genetics; D020871:RNA Stability / Q000235:genetics; D012342:RNA, Small Nuclear / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D000461:Rhodophyta / Q000235:genetics / Q000378:metabolism*; D017381:Spliceosomes / Q000378:metabolism*
D020418:Algal Proteins; D012322:RNA Precursors; D012342:RNA, Small Nuclear
U1 snRNP; genome reduction; pre-mRNA splicing; spliceosome core; splicing mechanism