Abstract

A hypothesis for the control of eukaryotic DNA replication at the chromosomal level is proposed. The specific regulatory problem arises from the subdivision of the genome into thousands of individually replicating units, each of which must be duplicated a single time during S‐phase. The hypothesis is based on the finding of direct repeats at replication origins. Such repeats can adopt, beyond the full‐length double helical structure, another configuration exposing two single‐stranded loops that provide suitable templates for the initiation of DNA replication. Any further initiation at the same origin is excluded as the single strandedness is eliminated by the replication process. Restoration of the initiable loop structure is proposed to occur by DNA‐protein rearrangements involved in chromosome condensation and duplication of the chromosomal protein backbone during mitosis. A possible role of the maturation promoting factor (MPF) is suggested.