Unusual properties of the DNA from Xanthomonas phage XP-12 in which 5-methylcytosine completely replaces cytosine.
Xanthomonas phage XP-12 contains 5-methylcytosine completely replacing cytosine. This substitution confers several unusual properties upon XP-12 DNA. The buoyant density of XP-12 DNA in CsCl gradients is 1.710 g/cm-3, 0.16 g/cm-3 lower than that expected for a normal DNA with the same percentage of adenine plus thymine. The melting temperature for XP-12 DNA in 0.012 M Na+ is the highest reported for any naturally occurring DNA, 83.2 degrees C, 6.1 degrees C higher than that of normal DNAs with the same percentage of adenine plus thymine. Unlike the minor amounts of 5-methylcytosine found in most plant and animal DNAs, the 5-methylcytosine residues of XP-12 derive their methyl group from the 3-carbon of serine instead of from the thiomethyl carbon of methionine.  .
D001435:Bacteriophages; D001483:Base Sequence; D002250:Carbon Radioisotopes; D002499:Centrifugation, Density Gradient; D003596:Cytosine / Q000031:analogs & derivatives* / Q000096:biosynthesis; D004279:DNA, Viral; D003720:Densitometry; D009691:Nucleic Acid Denaturation; D014316:Tritium; D014974:Xanthomonas
D002250:Carbon Radioisotopes; D004279:DNA, Viral; D014316:Tritium; D003596:Cytosine