Methylation pattern of mouse mitochondrial DNA

Abstract
The pattern of methylation of mouse mitochondrial DNA (mtDNA) was studied using several techniques. By employing a sensitive analytical procedure it was possible to show that this DNA contains the modified base 5-methylcytosine (m5Cyt). This residue occurred exclusively at the dinucleo-tide sequence CpG at a frequency of 3 to 5%. The pattern of methylation was further investigated by determining the state of methylation of several MspI(HpaII) sites. Different sites were found to be methylated to a different extent, implying that methylation of mtDNA is nonrandom. Based on the known base composition and nucleotide sequence of mouse mtDNA, the dinucleo-tide sequence CpG was found to be underrepresented in this DNA.