Pre-mRNA has both introns and exons. As a part of the maturation process, RNA splicing removes the non-coding RNA introns leaving behind the exons, which are then spliced and joined together to form the mature mRNA. Splicing is conducted by the spliceosome. The spliceosome is a large ribonucleoprotein which cleaves the RNA at the splicing site and recombines the exons of the RNA. Similar to polyadenylation, alternative splicing can occur, resulting in several possible proteins being translated from the same portion of DNA. See RNA Splicing for further details.