ABSTRACT
The primary ribonucleic acid (RNA) transcript from a protein-coding gene in a eukaryotic cell must be modified by several RNA processing reactions in order to become a functional messangerRNA (mRNA) molecule. Capping of pre-mRNA occurs immediately after synthesis and involves the addition of 7-methylguanosine to the 5' end. Most eukaryotic pre-mRNAs undergo polyadenylation which involves cleavage of the RNA at its 3' end and the addition of up to 250 A residues to form a poly(A) tail. Certain pre-mRNAs contain more than one set of signal sequences for 3' end cleavage and polyadenylation. In some cases, the location of the alternative polyadenylation sites is such that, depending on the site chosen, particular exons may be lost or retained in the subsequent splicing reactions. The effect of RNA editing is to change the coding capacity of the mRNA so that it encodes a different polypeptide than that originally encoded by the gene.
