RNA splicing , carried out by a complex called the spliceosome , is the process by which introns , or regions of DNA that do not code for protein , are removed from the pre @-@ mRNA and the remaining exons connected to re @-@ form a single continuous molecule . This process normally occur after 5 ' capping and 3 ' polyadenylation but can begin before synthesis is complete in transcripts with many exons . Many pred @-@ mRNAs , including those encoding antibodies , can be spliced in multiple ways to produce different mature mRNAs that encoded different protein sequences . This process is known as alternative splicing , and allow production of a large variety of proteins from a limited amount of DNA .