Crystallization and preliminary X-ray diffraction analysis of SeqA bound to a pair of hemimethylated GATC sites.

Escherichia coli SeqA is a negative regulator of DNA replication. The SeqA protein forms a high-affinity complex with newly replicated DNA at the origin of replication and thus prevents premature re-initiation events. Beyond the origin, SeqA is found at the replication forks, where it organizes newly replicated DNA into higher ordered structures. These two functions depend on SeqA binding to multiple hemimethylated GATC sequences. In an effort to understand how SeqA forms a high-affinity complex with hemimethylated DNA, a dimeric variant of SeqA was overproduced, purified and crystallized bound to a DNA duplex containing two hemimethylated GATC sites. The preliminary X-ray analysis of crystals diffracting to 3 A resolution is presented here.