The spliceosome is a multicomponent ribonucleoprotein complex that catalyzes the removal of introns from nuclear mRNA precursors. The spliceosome is composed of four small ribonucleoprotein particles (the U1, U2, and U4/U6 snRNPs) and numerous additional proteins. The U2 small nuclear RNA (snRNA) is a RNA component of the U2 snRNP that interacts with the 3' region of the intron at the branch site. Several sites in the human genome express U2 snRNAs. This locus represents an array of U2 snRNA genes located at 17q21-22 that undergoes concerted evolution to homogenize repeat units within the array. Each repeat in this array is approximately 6.1 kb long and contains a single copy of the U2 snRNA. Arrays of six to more than 30 repeats have been reported. (provided by RefSeq)