spliceosomal

Spliceosomal refers to the spliceosome, a large ribonucleoprotein complex responsible for removing introns from pre-messenger RNA in the majority of eukaryotes. Splicing joins exons to produce mature mRNA and releases a lariat-shaped intron. The spliceosome catalyzes two transesterification reactions and requires energy from RNA helicases.

Composition and assembly: The core includes five snRNPs (U1, U2, U4, U5, U6) with snRNA and proteins, plus numerous non-snRNP factors. Assembly occurs in stages (E, A, B, B*, C, C*) with U1 recognizing the 5' splice site, U2 binding the branch point, and the U4/U6.U5 tri-snRNP joining to form the catalytic core.

Mechanism and products: The first step uses the branch-point adenosine 2'-OH to attack the 5' splice site, creating a lariat intron and a 3'-exon–5' junction. The second step joins the exons and releases the intron lariat, which is degraded. The spliceosome is then recycled for subsequent rounds of splicing.

Regulation and significance: Spliceosomal activity is regulated by SR proteins and hnRNPs, enabling alternative splicing and transcript diversity. Defects in spliceosomal components or assembly factors can cause disease, including retinitis pigmentosa linked to PRPF gene mutations and other splicing-related disorders.