A Sm-like protein complex that participates in mRNA degradation

Abstract

In eukaryotes, seven Sm proteins bind to the U1, U2, U4 and U5 spliceosomal snRNAs while seven Smlike proteins (Lsm2p–Lsm8p) are associated with U6 snRNA. Another yeast Sm‐like protein, Lsm1p, does not interact with U6 snRNA. Surprisingly, using the tandem affinity purification (TAP) method, we identified Lsm1p among the subunits associated with Lsm3p. Coprecipitation experiments demonstrated that Lsm1p, together with Lsm2p–Lsm7p, forms a new sevensubunit complex. We purified the two related Sm‐like protein complexes and identified the proteins recovered in the purified preparations by mass spectrometry. This confirmed the association of the Lsm2p–Lsm8p complex with U6 snRNA. In contrast, the Lsm1p–Lsm7p complex is associated with Pat1p and Xrn1p exoribonuclease, suggesting a role in mRNA degradation. Deletions of LSM1, 6, 7 and PAT1 genes increased the half‐life of reporter mRNAs. Interestingly, accumulating mRNAs were capped, suggesting a block in mRNA decay at the decapping step. These results indicate the involvement of a new conserved Sm‐like protein complex and a new factor, Pat1p, in mRNA degradation and suggest a physical connection between decapping and exonuclease trimming.

Isolation and study of KlLSM4 , a Kluyveromyces lactis gene homologous to the essential gene LSM4 of Saccharomyces cerevisiae

“…These results were almost identical to those obtained in K. lactis and confirmed that the lack of the C-terminal region of the protein severely affects cell viability during the stationary phase. In S. cerevisiae, the role of Lsm4p has been associated with mRNA splicing and decapping (Bouveret et al, 2000;Mayes et al, 1999;Thaurun et al, 2000) and work is in progress to verify whether these processes are altered in the K. lactis and S. cerevisiae strains expressing the truncated form of KlLsm4p. Cells were grown on YPD medium and OD 600 was measured at the indicated times.…”

Ataxin-2 Interacts with the DEAD/H-Box RNA Helicase DDX6 and Interferes with P-Bodies and Stress Granules

“…These proteins colocalize in discrete cytoplasmic foci in mammalian cells, termed processing bodies or P-bodies (also known as DCP1-or GW182-bodies), indicating that mRNA decay is restricted to distinct cytoplasmic compartments in mammalian cells (van Dijk et al, 2002;Cougot et al, 2004). The human protein CCR4, which is involved in mRNA deadenylation, the decapping stimulating LSm proteins LSm1-7, the DEAD/Hbox RNA helicase DDX6 (also known as RCK/p54), GW182, and Ge-1 are components of P-bodies (Bouveret et al, 2000;Eystathioy et al, 2002;Ingelfinger et al, 2002; LykkeAndersen, 2002;Cougot et al, 2004;Yu et al, 2005). Moreover, the RNA-associated protein 55, hEDC3, Hedls as well as factors of the RISC complex localize to P-bodies in mammalian cells (Fenger-Gron et al, 2005;Liu et al, 2005;Sen and Blau, 2005;Yang et al, 2006).…”

Homomeric Ring Assemblies of Eukaryotic Sm Proteins Have Affinity for Both RNA and DNA

“…The most highly characterized Sm/Lsm-containing RNPs are those involved in pre-mRNA splicing, the U1, U2, U4/U6, and U5 small nuclear RNPs (snRNPs) (1), whereas others are known to be important for telomere replication (2), trans-splicing (3), and mRNA degradation (4,5).…”