SMN1 Protein, Human (His)

The SMN complex catalyzes the assembly of small nuclear ribonucleoproteins (snRNPs), the building blocks of the spliceosome, playing a crucial role in the splicing of cellular pre-mRNAs. Most spliceosomal snRNPs contain a common set of Sm proteins (SNRPB, SNRPD1, SNRPD2, SNRPD3, SNRPE, SNRPF, and SNRPG) that assemble into a heptameric protein ring on the Sm site of small nuclear RNA to form the core snRNP (Sm core). In the cytosol, the Sm proteins SNRPD1, SNRPD2, SNRPE, SNRPF, and SNRPG are trapped in an inactive 6S pICln-Sm complex by the chaperone CLNS1A, which regulates core snRNP assembly. The SMN complex accepts the trapped 5Sm proteins from CLNS1A to form an intermediate, with SMN1 acting as a structural backbone alongside GEMIN2 to gather Sm complex subunits. Binding of snRNA within 5Sm triggers the eviction of the SMN complex, allowing SNRPD3 and SNRPB to complete core snRNP assembly. The SMN complex also ensures proper splicing of U12 intron-containing genes, which may be important for normal motor and proprioceptive neuron development. Additionally, it resolves RNA-DNA hybrids formed by RNA polymerase II, which create R-loops in transcription termination regions, a critical step in proper transcription termination. It may also play a role in small nucleolar ribonucleoprotein (snoRNPs) metabolism.