Replication timing is regulated by the number of MCMs loaded at origins

Reducing MCM loading delays the timing of origin firing. (A) Western blot as in Figure 2A from G1-arrested cells carrying an ARS1- (yFS853) or ARS1-ΔB2- (yFS854) containing TALO8 plasmid. (B) Quantitation of data in A: n = 7 for ARS1, n = 5 for ARS1-ΔB2, error bars represent SEM. (C) Replication timing of eight origins in cells with chromosomal alleles of ARS1 (yFS833) or ARS1-ΔB2 (yFS842). Cells were released from α-factor and sampled at various times during S phase. The copy number of each locus was assayed using a NanoString nCounter: n = 2 for ARS1 and ARS1-ΔB2, n = 4 for other origins. The inset table lists the average replication time (t_rep ± SEM) for each origin analyzed.