The sole LSm complex inCyanidioschyzon merolaeassociates with pre-mRNA splicing and mRNA degradation factors.
Proteins of the Sm and Sm-like (LSm) families, referred to collectively as (L)Sm proteins, are found in all three domains of life and are known to promote a variety of RNA processes such as base-pair formation, unwinding, RNA degradation, and RNA stabilization. In eukaryotes, (L)Sm proteins have been studied, inter alia, for their role in pre-mRNA splicing. In many organisms, the LSm proteins form two distinct complexes, one consisting of LSm1-7 that is involved in mRNA degradation in the cytoplasm, and the other consisting of LSm2-8 that binds spliceosomal U6 snRNA in the nucleus. We recently characterized the splicing proteins from the red algaCyanidioschyzon merolaeand found that it has only seven LSm proteins. The identities of CmLSm2-CmLSm7 were unambiguous, but the seventh protein was similar to LSm1 and LSm8. Here, we use in vitro binding measurements, microscopy, and affinity purification-mass spectrometry to demonstrate a canonical splicing function for theC. merolaeLSm complex and experimentally validate our bioinformatic predictions of a reduced spliceosome in this organism. Copurification of Pat1 and its associated mRNA degradation proteins with the LSm proteins, along with evidence of a cytoplasmic fraction of CmLSm complexes, argues that this complex is involved in both splicing and cytoplasmic mRNA degradation. Intriguingly, the Pat1 complex also copurifies with all four snRNAs, suggesting the possibility of a spliceosome-associated pre-mRNA degradation complex in the nucleus.
Department of Chemistry, University of Northern British Columbia, Prince George, BC V2N 4Z9, Canada.
Kirsten A
0000-0002-5183-6110
KA
Reimer
Department of Chemistry, University of Northern British Columbia, Prince George, BC V2N 4Z9, Canada.
Martha R
MR
Stark
Laboratory of RNP Biochemistry, Institut de Recherches Cliniques de Montréal (IRCM), Faculty of Medicine, McGill University, Montreal, QC H3A 0G4, Canada.
Lisbeth-Carolina
0000-0002-7296-3733
LC
Aguilar
Department of Chemistry, University of Northern British Columbia, Prince George, BC V2N 4Z9, Canada.
Sierra R
SR
Stark
Department of Biochemistry and Microbiology, University of Victoria, Victoria, BC, V8W 3P6, Canada.
Robert D
0000-0001-5527-4410
RD
Burke
Department of Biochemistry, University of Alberta, Edmonton, Alberta T6G 2H7, Canada.
Jack
J
Moore
Department of Biochemistry, University of Alberta, Edmonton, Alberta T6G 2H7, Canada.|Department of Oncology, University of Alberta, Edmonton, Alberta T6G 2H7, Canada.
Richard P
RP
Fahlman
Department of Biochemistry and Molecular Biology, The University of British Columbia, Vancouver, BC V6T 1Z3, Canada.
Calvin K
0000-0003-1779-9501
CK
Yip
Kuroiwa Initiative Research Unit, College of Science, Rikkyo University, Toshima, Tokyo 171-8501, Japan.
Haruko
H
Kuroiwa
Laboratory of RNP Biochemistry, Institut de Recherches Cliniques de Montréal (IRCM), Faculty of Medicine, McGill University, Montreal, QC H3A 0G4, Canada.|Département de Biochimie, Université de Montréal, Montréal, QC H2W 1R7, Canada.
Marlene
0000-0001-6427-1393
M
Oeffinger
Department of Chemistry, University of Northern British Columbia, Prince George, BC V2N 4Z9, Canada.
Stephen D
0000-0001-7242-1785
SD
Rader
D000595:Amino Acid Sequence; D001483:Base Sequence; D019295:Computational Biology / Q000379:methods; D047468:Immunoprecipitation; D008958:Models, Molecular; D009690:Nucleic Acid Conformation; D010802:Phylogeny; D011485:Protein Binding; D011487:Protein Conformation; D021381:Protein Transport; D012322:RNA Precursors / Q000737:chemistry / Q000235:genetics*; D012326:RNA Splicing; D020871:RNA Stability; D012333:RNA, Messenger / Q000737:chemistry / Q000235:genetics*; D012342:RNA, Small Nuclear / Q000737:chemistry / Q000235:genetics; D016601:RNA-Binding Proteins / Q000737:chemistry / Q000378:metabolism*; D000461:Rhodophyta / Q000235:genetics* / Q000378:metabolism*; D053719:Tandem Mass Spectrometry
D012322:RNA Precursors; D012333:RNA, Messenger; D012342:RNA, Small Nuclear; D016601:RNA-Binding Proteins; C405486:U6 small nuclear RNA
Cyanidioschyzon merolae; LSm complex; Pat1; U6 snRNA; mRNA degradation; pre-mRNA splicing