Repli-seq of early S phase fraction: WT  mESC
Genome-wide RT profiles were constructed as  previously described. Briefly, cells were pulse labeled with BrdU for 2 hours  and separated into early and late S-phase fractions by Propidium iodide  staining and flow cytometry. BrdU-substituted DNA from 40k early and late  S-phase cells was immunoprecipitated by anti-BrdU antibody (Becton Dickinson  347580)Sequencing libraries were prepared by NEBNext Ultra DNA Library Prep  Kit for Illumina (E7370).