A. Experimental scheme and representative images of DNA fibers. Scale bar: 5 μm.B. Analysis of fibers showing proportions of replication forks that showed restart after HU treatment or remained stalled. N=2, >500 fibers scored per experiment.C. Proportion of total forks showing de novo initiation after HU treatment. N=2, >500 fibers scored per experiment.D. Length of initial replication fork tracts (CldU tracts). N=2, >200 fibers measured per experiment. 