Different splice variants exists due to alternative splicing. SR proteins are important for selecting splice sites for alternative splicing. In mRNA, codons also work as exon splicing enhancers. The RNA that results from RNA splicing is a sequence of exons. Noncoding RNA also contributes to epigenetics, transcription, RNA splicing, and the translational machinery. Integrin beta-1 can exist as different isoforms via alternative splicing. HBII-52 regulates the splicing of serotonin receptor 2C. GluN1 has eight different isoforms due to alternative splicing of the gene GRIN1. SR proteins are a conserved family of proteins involved in RNA splicing. B cells may express IgD by alternative RNA splicing and class switch recombination. It is an antisense nucleotide that modifies the alternative splicing of the "SMN2" gene. This mutation interrupts a site of RNA splicing. CpG DNA methylation has showed a role to regulate the alternative splicing in social insects. The BPS contains the conserved adenosine required for the first step of splicing. One study involved estrogen receptors and differential splicing.