Beyond homing: competition between intron endonucleases confers a selective advantage on flanking genetic markers.
The closely related B. subtilis bacteriophages SPO1 and SP82 have similar introns inserted into a conserved domain of their DNA polymerase genes. These introns encode endonucleases with unique properties. Other intron-encoded "homing" endonucleases cleave both strands of intronless DNA; subsequent repair results in unidirectional gene conversion to the intron-containing allele. In contrast, the enzymes described here cleave one strand on both intron-containing and intronless targets at different distances from their common intron insertion site. Most surprisingly, each enzyme prefers DNA of the heterologous phage. The SP82-encoded endonuclease is responsible for exclusion of the SPO1 intron and flanking genetic markers from the progeny of mixed infections, a novel selective advantage imparted by an intron to the genome in which it resides.
Goodrich-Blair
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Department of Biological Sciences, State University of New York at Albany 12222, USA.
Shub
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DA
D017103:Bacillus Phages / Q000201:enzymology* / Q000235:genetics; D001412:Bacillus subtilis / Q000821:virology; D001483:Base Sequence; D003001:Cloning, Molecular; D004262:DNA Restriction Enzymes / Q000235:genetics* / Q000378:metabolism*; D004279:DNA, Viral / Q000378:metabolism; D004259:DNA-Directed DNA Polymerase / Q000235:genetics; D005819:Genetic Markers; D007438:Introns; D008969:Molecular Sequence Data; D016366:Open Reading Frames / Q000235:genetics; D010432:Pentoxyl / Q000031:analogs & derivatives / Q000378:metabolism; D013379:Substrate Specificity
D004279:DNA, Viral; D005819:Genetic Markers; C008055:5-hydroxymethyluracil; D010432:Pentoxyl; D004259:DNA-Directed DNA Polymerase; D004262:DNA Restriction Enzymes