What are spliceosomes?

Spliceosomes are large complexes found in the nucleus of eukaryotic cells. They assemble on RNA transcripts produced by RNA polymerase II and remove introns. They then join together with exons to form mature mRNA molecules in a process called pre-messenger RNA (pre-mRNA) splicing. This splicing is crucial for the synthesis of functional mRNA in eukaryotic cells. Each human cell contains around 100,000 spliceosomes, which collectively remove over 200,000 different intron sequences. There are two types of spliceosomes in human cells: the major spliceosome (which removes the majority of introns) and the minor spliceosome (which removes a small fraction of introns).