PARP1 mediates H1 mobility and IEG expression in stimulated PMNs. (A–D) FRAP analysis of H1.0-GFP on depolarized (KCl) or unstimulated (NaCl) PMNs in WT (A), Parp1^−/− (B), Parp2^−/− (C), and Parp1/Parp2-DKO cells (D). FRAP experiments were done on at least 20–30 cells, and all experiments were repeated at least twice. Error bars represent standard deviation (*, P < 0.0001 [A], P < 0.05 [B], P < 0.0005 [C], and P < 0.05 [D]; two-tailed Student’s t test); the dynamic response to KCl is significantly lower in PARP1-KO and PARP1/PARP2-KO cells than in WT cells; P < 0.05). (E and F) quantitative real-time PCR for c-Fos (E) and Egr1 (F) in resting (NaCl) and depolarized (KCl) PMNs (cortical neurons) in WT and KO out cells as indicated. Error bars represents standard deviation. (G) FRAP experiments (on at least 20–30 cells) for GFP-H1e in which all putative PARylation sites have been converted to alanines, in resting (NaCl) or depolarized (KCl) wild-type PMNs. Error bars represent standard deviation. The typical increased mobility of H1 after KCl stimulation is prevented in the PARylation-mutated H1.