Bacteriophage introns: parasites within parasites?

Several bacteriophage introns carry the information necessary to perform a complex series of RNA as well as DNA rearrangements. The RNA splicing reactions allow expression of the intron-containing genes, whereas recombination at the DNA level results in the mobility and invasive potential of the introns. The RNA and DNA transactions are temporally regulated to permit timely splicing early in infection, and expression of intron-encoded DNA endonucleases involved in mobility at late times. This is achieved through efficient use of the viral regulatory machinery, ensuring the perpetuation of the 'parasitic' introns.