Fall 2009 MCDB Seminar - Dr. David Shub - SUNY- Albany, NY

Selfish DNA Meets Catalytic RNA: group I introns and their homing endonucleases.

Well before the splicing properties and catalytic activities of their RNA transcripts were discovered, yeast geneticists had identified group I introns as loci of unidirectional gene conversion.  Many group I introns are mobile, and his mobility is conferred by a gene for a site-specific DNA endonuclease that is embedded in the intron.  However, the relationship between an intron and its “homing” endonuclease is not stable: endonucleases are gained and lost over time, and the endonuclease genes themselves behave as mobile genetic elements, even in the absence of an intron home.  Homing endonucleases are particularly abundant in bacteriophage genomes, where they likely play an important role in generation of genetic variation by stimulating recombination in related phages, and between phages and their bacterial hosts.  A particularly surprising recent discovery is that, rather than landing only in group I introns, homing endonuclease genes can also be inserted within coding sequences of essential genes, splitting one gene into two independently translated genes whose protein products assemble to recreate a functional enzyme.  This talk will review various genomic relationships that have recently come to light between homing endonuclease genes, group I introns, and other RNA elements.