Splicing and the RNAi mechanism regulate which mRNA molecules are translated via small RNA molecules like siRNA and snRNA. siRNA and snRNA contain uridine and are around 150 nucleotides, forming spliceosomes to splice with the help of snRNP. MicroRNAs are 21-27 nucleotide non-coding products that cause gene silencing by binding to the 3' UTR of mRNA and inhibiting translation. Both miRNA and siRNA can silence gene expression by cleavage or base pairing with mRNA. Dicer is an endoribonuclease that cleaves long double-stranded RNA and pre-microRNA into 20-25 nucleotide fragments, producing small interfering RNA and microRNA which influence gene expression.