The archaeal Sm-like (LSm): The Sm proteins are conserved in all three domains of life and are always associated with U-rich RNA sequences. They function to mediate RNA-RNA interactions and RNA biogenesis. All Sm proteins contain a common sequence motif in two segments, Sm1 and Sm2, separated by a short variable linker. Eukaryotic Sm proteins form part of specific small nuclear ribonucleoproteins (snRNPs) that are involved in the processing of pre-mRNAs to mature mRNAs, and are a major component of the eukaryotic spliceosome. Most snRNPs consist of seven Sm proteins (B/B', D1, D2, D3, E, F and G) arranged in a ring on a uridine-rich sequence (Sm site), plus a small nuclear RNA (snRNA) (either U1, U2, U5 or U4/6). Since archaebacteria do not have any splicing apparatus, their Sm proteins may play a more general role. Archaeal LSm proteins are likely to represent the ancestral Sm domain. Members of this family share a highly conserved Sm fold containing an N-terminal helix followed by a strongly bent five-stranded antiparallel beta-sheet. Sm-like proteins exist in archaea as well as prokaryotes that form heptameric and hexameric ring structures similar to those found in eukaryotes.
Comment:by similarity to other members of this superfamily
Comment:This oligomerization interface is flexible and plays a role in both the hexameric arrangement of assembly intermediates and the hetero-heptamer
Jiyao W et al.(2023). "The conserved domain database in 2023.",