THE INS AND OUTS OF PROTEIN SPLICING ELEMENTS

Protein splicing involves the removal of an internal protein sequence from a precursor molecule and the ligation of the two flanking sequenc es to produce a mature protein product, in a post-translational event analogous to the removal of an intron from rRNA. Protein splicing intr ons, or 'inteins' appear to be a novel type of genetic element capable of mediating gene conversion of an 'intein-less' allele, and hence pr omoting their own dissemination. The mechanism by which protein splici ng is achieved is probably entirely encoded within the internal protei n sequence, or intein, and does not require other accessory molecules. Although the concept of protein splicing inteins as selfish genetic e lements of no immediate consequence to the host organism has emerged, this interpretation is questioned by recent evidence that in at least one example there appears to have been selection for protein splicing.