Replication fork and checkpoint levels regulate replication fork progression. (A) Genome-wide origin firing and local fork rate for the experiments in MMS are plotted; mean and standard deviation are shown (n = 2). Data points are color coded for the experimental group represented. (B) The model depicts fork rate regulation in WT and mutant strains with different levels of origin firing and checkpoint functions. The font intensities and line/arrow thicknesses represent the relative strength of the corresponding pathway or signal. For example, gray fonts indicate a weak or defective function or pathway, and bold fonts indicate a hyperactive function or pathway. The chromosome graphic below each model depicts the levels of origin firing and fork rate in each condition. Open circles represent fired origins, and filled circles represent unfired origins; E, M, and L indicate early, middle, and late firing origins, respectively.