Methylation of GATC sites is required for precise timing between rounds of DNA replication in Escherichia coli.

AUTOR(ES)

Bakker, A

RESUMO

We have used the Koppes and Nordstrøm (Cell 44:117-124, 1986) CsCl density transfer approach for analysis of DNA from exponentially growing, isogenic Escherichia coli dam+ and dam mutant cells to show that timing between DNA replication initiation events is precise in the dam+ cells but is essentially random in the dam cells. Thus, methylation of one or more GATC sites, such as those found in unusual abundance within the origin, oriC, is required for precise timing between rounds of DNA replication, and precise timing between initiation events is not required for cell viability. Both the dam-3 point mutant and the delta(dam)100 complete deletion mutant were examined. The results were independent of the mismatch repair system; E. coli mutH cells showed precise timing, whereas timing in the isogenic E. coli mutH delta(dam)100 double mutant was random. The mechanism is thus different from the role of Dam methylation in mismatch repair and probably involves conversion of hemimethylated GATC sites present in daughter origins just after initiation to a fully methylated state.

Documentos Relacionados

• Importance of state of methylation of oriC GATC sites in initiation of DNA replication in Escherichia coli.
• Termination of DNA replication is required for cell division in Escherichia coli.
• Arrangement of Dam methylation sites (GATC) in the Escherichia coli chromosome.
• Escherichia coli cells lacking methylation-blocking factor (leucine-responsive regulatory protein) have precise timing of initiation of DNA replication in the cell cycle.
• Biological role of DNA methylation: sequence-specific single-strand breaks associated with hypomethylation of GATC sites in Escherichia coli DNA.