title: Bacteriophage XP-12-induced exonuclease which preferentially hydrolyzes nicked DNA.
abstract: An exonuclease has been partially purified from XP-12-infected Xanthomonas oryzae which is not found in uninfected X. oryzae. Although both the phage-induced exonuclease and the major host exonucleolytic DNase released 5'-mononucleotides, these enzymes differed in their chromatographic behavior, pH optimum, salt inhibition, and heat sensitivity. These two exonucleases preferred different substrates. Nicked native DNA was the best substrate for the phage-induced enzyme, whereas denatured DNA was the best substrate for the host enzyme. Also, the host enzyme had a significant preference for denatured or nicked, normal cytosine-containing DNA (e.g., X. oryzae or T7 DNA) over similarly denatured or nicked 5-methylcytosine-rich DNA (namely, XP-12DNA), whereas the phage-induced enzyme hydrolyzed both types of DNA equally well.
mesh_terms: D044503:5-Methylcytosine; D001435:Bacteriophages / Q000032:analysis / Q000201:enzymology*; D002848:Chromatography, DEAE-Cellulose; D003596:Cytosine / Q000031:analogs & derivatives / Q000378:metabolism; D004269:DNA, Bacterial / Q000378:metabolism; D004279:DNA, Viral / Q000378:metabolism; D005092:Exonucleases / Q000302:isolation & purification*; D013379:Substrate Specificity; D014974:Xanthomonas / Q000201:enzymology*
chemical_list: D004269:DNA, Bacterial; D004279:DNA, Viral; D044503:5-Methylcytosine; D003596:Cytosine; D005092:Exonucleases