The two essential components of snRNPs are protein molecules and RNA. The RNA found within each snRNP particle is known as small nuclear RNA, or snRNA, and is usually about 150 nucleotides in length. The snRNA component of the snurp is specific to individual introns because it 'recognises' the sequences of critical signals at the ends and branch sites of introns. The snRNA in snurps is similar to ribosomal RNA: it acts both as an enzyme (catalyst) and builds structure.