GATC

GATC is a short DNA sequence motif, 5'-GATC-3', that functions as a common recognition site in bacterial genomes. The motif is a palindrome, so the sequence is the same on the complementary strand, and it is methylated on the adenine within the site by the DNA adenine methyltransferase (Dam) in many bacteria, notably Escherichia coli and other Gammaproteobacteria. Dam methylation produces N6-methyladenine (m6A) at GATC sites and creates a genome-wide methylation pattern that can be inherited during cell division.

Methylation of GATC plays several key roles. The mismatch repair system uses the difference between methylated parental strands and newly synthesized, unmethylated daughter strands to distinguish the strand to be repaired. After replication, SeqA binds hemimethylated GATC sites to delay initiation of a new round of replication at oriC until methylation occurs. Dam methylation also modulates transcription of a subset of genes, including some virulence and phase-variable loci, by altering promoter accessibility or protein binding.

Restriction-modification systems exploit recognition of GATC. Some enzymes cut only unmethylated GATC, while others, such as DpnI, cleave specifically methylated GATC, enabling applications in molecular cloning and DNA analysis that differentiate methylation states.

Although widespread in many bacteria, Dam methylation is not universal. Some species lack Dam or use alternative methylation schemes, and eukaryotes generally rely on CpG methylation rather than adenine methylation.