Genes can generate a wide range of mature RNA variants through the alternative splicing process (1,2). In fact, studies have revealed that virtually all multi-exon human genes (3,4) are capable of producing at least two RNA transcripts by alternative splicing. Alternative splicing events that occur within coding regions will produce alternative transcripts that have the potential to be translated into distinct gene products. Those alternative transcripts that are not picked up by the cellular surveillance machinery, such as nonsense-mediated decay (NMD; 5,6), non-stop decay (7) and no-go decay (8), may contribute to an increase in the complexity of the cell. Alternative gene products often have a surprising level of diversity (9) and can therefore have very different biological and cellular properties. Thus, the suggestion that the rearrangement of exons conducted by alternative splicing may enrich the repertoire of cellular functions (10).
