Mechanism of Paf1/PD2 in the maintenance of ESCs. (A): Reciprocal immunoprecipitation of Paf1/PD2, Oct3/4, and RNA Pol II in mouse ESCs. (B): The ChIP-Re-ChIP analysis for Oct3/4 and PD2 in embryonic stem cells. ChIP-Re-ChIP DNA was used to amplify FGF-4, Nanog, and Lefty-1 promoter fragment by SYBR Green QPCR analysis. The nonspecific primers were not amplified in any of the three genes. MUC4 antibody was used as a control antibody. The fold enrichment of FGF-4, Nanog, and Lefty-1 is related to MUC4 control antibody. (C): Mechanisms through which Oct3/4-PD2 interaction can regulate Oct3/4-mediated gene expression. A protein-protein interaction between Oct3/4 and Paf1/PD2 may have different possible implications through which Oct3/4-mediated gene expression can be regulated. An interaction between Oct3/4 with Paf1/PD2 may help to regulate expression of a subset Oct3/4 target genes such as FGF-4, Nanog, and Lefty-1 for the maintenance of ESCs. Abbreviations: Ab, antibody; C-r-C, sequential chromatin immunoprecipitations with two antibodies to study the simultaneous presence of two proteins in the genome sequence of interest; IB, immunoblot; IP, immunoprecipitation; Pol II, polymerase II.