Component of LSM protein complexes, which are involved in RNA processing. Component of the cytoplasmic LSM1-LSM7 complex which is involved in mRNA degradation by promoting decapping and leading to accurate 5'-3' mRNA decay. The cytoplasmic LSM1-LSM7 complex regulates developmental gene expression by the decapping of specific development-related transcripts. Component of the nuclear LSM2-LSM8 complex which is involved splicing nuclear mRNAs. LSM2-LSM8 binds directly to the U6 small nuclear RNAs (snRNAs) and is essential for accurate splicing of selected development-related mRNAs through the stabilization of the spliceosomal U6 snRNA. Plays a critical role in the regulation of development-related gene expression. Component of the heptameric LSM1-LSM7 complex that forms a seven-membered ring structure with a donut shape. The LSM subunits are arranged in the order LSM1, LSM2, LSM3, LSM6, LSM5, LSM7 and LSM4. Component of the heptameric LSM2-LSM8 complex that forms a seven-membered ring structure with a donut shape. The LSM subunits are arranged in the order LSM8, LSM2, LSM3, LSM6, LSM5, LSM7 and LSM4 (PubMed:23221597, PubMed:23620288). LSM3A subunit interacts only with its two neighboring subunits, LSM2 and LSM6A or LSM6B (PubMed:23221597). Expressed in roots, leaves, stems, flowers and siliques. Belongs to the snRNP Sm proteins family.