HOMING SWEET HOMING - MOBILE INTRONS IN BACTERIAL-VIRUSES

Several bacteriophage group I introns are self-splicing at the RNA lev el, while they behave as mobile genetic elements at the DNA level. Con tained within the catalytic RNAs are open reading frames which encode endonucleases that initiate the intron mobility reaction. This process , called homing, is a gene conversion went whereby an intron transfers from an intron-plus allele to the cognate intron-minus allele. Such m obile introns are phylogenetically diverse, being found in both prokar yotic and eukaryotic genomes. In this context, the accessibility of th e phage systems and the unusual nature of the phage endonuclease:targe t site interactions make them a rewarding focus of study. We will disc uss the mobility process and the hierarchy of relationships between th e bacteriophage, its group I introns and the intron-encoded endonuclea ses.