Lsm1Lsm7

Lsm1-7 (often written Lsm1Lsm7 in shorthand) refers to the cytoplasmic heptameric ring composed of the Sm-like proteins Lsm1, Lsm2, Lsm3, Lsm4, Lsm5, Lsm6, and Lsm7. It is a key component of the eukaryotic mRNA decay machinery and is distinct from the Lsm2-8 complex, which operates in the nucleus with U6 snRNA. In many organisms, Lsm1-7 localizes to the cytoplasm and accumulates in processing bodies (P-bodies) where mRNA turnover is coordinated.

Structure and interactions: The Lsm1-7 complex forms a circular Sm-like ring that binds RNA, with a preference for 3' ends following deadenylation. The ring interacts with other decay factors, including the decapping enzymes DCP1 and DCP2, and accessory proteins such as Pat1 and Edc3. This network facilitates recruitment of the decapping machinery to targeted mRNAs and promotes subsequent 5' to 3' exonucleolytic decay by Xrn1.

Function and significance: The primary role of Lsm1-7 is to enhance mRNA decapping and turnover after deadenylation, thereby accelerating cytoplasmic mRNA decay and contributing to gene expression regulation and stress responses. By modulating RNA stability, the complex influences transcriptomes and is involved in RNA quality control. It is conserved across eukaryotes, with genetic or functional perturbations in Lsm1-7 affecting mRNA stability and cellular fitness in model organisms.

Evolution and context: Lsm1-7 is part of the broader Sm/Lsm protein family. While Lsm2-8 forms a nuclear complex essential for U6 snRNA stability and splicing, Lsm1-7 operates primarily in the cytoplasm to regulate cytoplasmic mRNA life cycle and decay processes.