Plays a role in pre-mRNA splicing as a core component of the spliceosomal U1, U2, U4 and U5 small nuclear ribonucleoproteins (snRNPs), the building blocks of the spliceosome (By similarity). Involved in germline establishment and development (PubMed:20570937, PubMed:20659974). Component of the osk mRNP (PubMed:20570937). Interacts with stau and yps (PubMed:20570937). Interacts with csul (via the N-terminal region) (PubMed:17164419). Interacts with vls (PubMed:17164419). Interacts (methylated) with tud (PubMed:17164419). Interacts with Smn; this interaction may be favored by SmB methylation (PubMed:16753561). Interacts with the SMN complex (PubMed:18621711). Interacts with msk and Snup; these interactions are RNA-dependent (PubMed:23885126). Expressed in the posterior part of the oocyte and embryo. Expressed in the pole plasm (at protein level), colocalizing with SmD3. Maternally and zygotically expressed. In early stages of egg chamber development, predominantly accumulated in the nuclei of nurse cells and oocyte. Enriched at the posterior of stage 10 oocytes which persists after fertilization, at the posterior of pre-blastoderm stage embryos. Symmetrically dimethylated on arginine residues present in the RG repeats by csul (or csul-vls complex) and Art7; methylation is not required for assembly and biogenesis of snRNPs, but required for pole plasm localization. There seems to be a specific role of two subsets of arginine residues in the C-terminal region: the subset containing Arg-112, Arg-130 and Arg-145 is required during embryogenesis for gonad formation, whereas the subset containing Arg-174, Arg-181, Arg-189 and Arg-196 is involved in pole cell formation by controlling polar granule maintenance at the posterior pole of the oocyte. Belongs to the snRNP SmB/SmN family.