(J). Replacement of this histidine by alanine on PARP1 or replacement of the YYR motif of KLF4 by triple alanines leads to the attenuation of KLF4 PARylation. In PARP1-/- MEFs, wild-type or mutant PARP1 (H909A) were co-transfected with FLAG-tagged wild-type or KLF4-Zinc 2-YYR/AAA mutation followed by immunoprecipitation using M2-agarose and Western blotting by anti-PAR antibody. 