Which chromatin replicates late?
Replication timing correlates tightly with chromatin state and transcriptional activity. Euchromatin, being open, acetylated and gene rich, replicates early in S phase when dNTP pools high and origin recognition complex easily loads. Constitutive heterochromatin, highly condensed with H3K9 trimethylation, HP1 oligomers, late-firing origins and peripheral nuclear lamina anchoring, replicates late in S phase. Autoradiography using tritiated thymidine and modern Repli-seq show satellite DNA incorporates label late. Facultative heterochromatin replicates mid to late, but constitutive blocks repres
Ref: Alberts et al., Molecular Biology of the Cell, 7th ed., Chapter 5: DNA Replication Timing - Heterochromatin Late Replicating
