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 sequences to produce a mature protein product, in a post-translational event analogous to the removal of an intron from rRNA. Protein splicing introns, or 'inteins' appear to be a novel type of genetic element capable of mediating gene conversion of an 'intein-less' allele, and hence promoting their own dissemination. The mechanism by which protein splicing is achieved is probably entirely encoded within the internal protein sequence, or intein, and does not require other accessory molecules. Although the concept of protein splicing inteins as selfish genetic elements 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.