It came to the authors' attention that in the original paper, an incorrect conversion factor was used for the pixel to micrometre conversion when analysing microscope images of combed fibres. The conversion factor used was 7.2 pixels = 1 lm instead of 13.9 pixels = 1 lm.The authors have re-analysed the affected data with the correct conversion factor of 13.9 pixels = 1 lm, applying the same criteria and cut-offs for tract assessment described in the original text. The re-analysis does not lead to any change in the conclusions from the experiments (i.e. rif1Δ delete and rif1-Δ C594 truncation mutants show nascent DNA degradation as originally described). As a consequence of this re-assessment, we have updated the sentence:"At 0 h (the time of HU addition), all three strains showing IdUlabelled tract of median length around 18 kb, consistent with an early stage of S phase when only some origins have initiated and bidirectional forks have travelled, on average, 9 kb each ( Fig 5C)." to read: "At 0 h (the time of HU addition), all three strains showing IdUlabelled tract of median length around 11.6 kb, consistent with an early stage of S phase when only some origins have initiated and bidirectional forks have travelled, on average, 5.8 kb each (Fig 5C)." and the sentence: "In rif1D cells, the nascent DNA tracts were in contrast noticeably eroded during the HU incubation period, with the median length decreasing from 21 to 13 kb in the first hour of the HU block." B IdU IdU C RIF1 rif1 rif1-C594 IdU tract length (kb) 0 20 40 60 0 1 1.5 0 1 1.5 0 1 1.5 hr in HU Figure 5B and C. Corrected figure. B IdU IdU C RIF1 rif1 rif1-C594 IdU tract length Figure 5B and C. Original figure.