Knockdown of SMARCA5 decreases replication fork velocity. A. Western analysis of whole cell extract prepared from HeLa cells transfected with either non-targeting (NT) siRNA or SMARCA5 siRNA at 72 h time point following transfection. Histone deacetylase 1 (Hdac1) and β-actin serve as loading controls. Replication fork velocity was measured in HeLa cells transfected with either non-targeting (NT) or SMARCA5 siRNA at 72 hr time point following transfection. Box plots from were derived from data obtained in three independent experiments. Representative DNA fibers are shown in the left panel. B. Model for the functions of Hdacs1,2 during DNA replication. Hdacs1,2 and SMARCA5 interact with proliferating cell nuclear antigen (PCNA) and recruited to forks during replication. Hdacs1,2 deacetylate H4K5ac, H4K12ac and H4K16ac. H4K12ac and H4K16ac inhibit SMARCA5 nucleosome remodeling activity. Deacetylation restores chromatin structure allowing proper inter-nucleosomal interactions and remodeler-driven nucleosome positions to support the progression of the replication fork. Green line, newly replicated DNA. Orange disk, nucleosome with histone tail(s). Blue circle, acetyl group.