The SET1 complex is responsible for maintaining H3K4 methylation and other active modifications to protect the 5′HS4-insulated transgene. (A) Schematic representation of the insulated IL2R transgene, which contains 4 copies, in the 6C2 genome (line 809), and the position of PCR primer sets used in ChIP analysis. (B-F) ChIP analysis of the flanking 5′HS4 sites and the integrated IL2R transgenes comparing the pSuper control infected and SET1 KD 809 cells. The relative enrichment of precipitated DNA fragments using antibodies specific to H3K4me2 (B), H3K9K14ac (C), BPTF (D), H3K9 dimethylation (E), and H3K27me3 (F) were normalized to enrichment of the endogenous HSA or 16-kb condensed chromatin fragments to adjust for immunoprecipitation efficiency. *P < .01 by Student t test. Shown are the means ± SEM of 3 independent experiments.