Nucleic Acids Research, 1985, Vol. 13, No. 4 1399-1412
© 1985
Articles |
DNA methylation in thermophilic bacteria: N4-methylcytosine, 5-methylcytosine, and N5methyladenine
Department of Biochemistry, Tulane Medical School New Orleans, LA 70112 1Department of Biochemistry, University of Georgia Athens, GA 30602 2Department of Biochemistry, Experiment Station Chemical Laboratories, University of Missouri Columbia, MO 65201, USA
Received November 14, 1984. Revised January 18, 1985. Accepted January 18, 1985.
While determining the minor and major base composition of the DNA from 17 types of thermophilic bacteria by high performance liquid chromatography (HPLC) of enzymatic digests, we have discovered a novel base, N4-nethylcytosine (m4C) Its structure was proven by comparison of the DNA-derived nucleoside to the analogous authentic compound by HPLC, UV spectroscopy, and mass spectroscopy. Eight of the bacterial DNAs contained m4C. Only two contained the common minor base, 5-methylcytosine (m5C) and neither of these was from an extreme thermophile. The other prevalent modified base of bacterial DNA, N6-methyladenine (m6A) was found in nine of the DNAs. Restriction analysis revealed that four of the DNAs had dam-type (Gm6ATC) methylation patterns. Due to the propensity of m5 residues to be deaminatad by heat to thymine residues and to inefficient repair of the resulting mismatched base pairs, thermophiles with optimal growth temperatures of 
60°C generally may avoid having m5C in their genomes. Instead, some of them have deamination-resistant m4C residues.