A semi-quantitative chromatin immunoprecipitation (ChIP) assay was performed to analyze Egr-1 binding to ORF50P in a chromatin context (in vivo) using specific antibodies. TPA-induced KSHV-infected cells were used to assess the binding ability of Egr-1 to ORF50P via ChIP assays. The presence of specific ORF50P in the IP samples was analyzed by semiquantitative PCR using specific primers covering the regions of ORF50P3 or ORF50P8. As expected, when Egr-1 was expressed in BCBL-1 cells it was recruited to the promoter of KSHV ORF50 and specifically targeted both ORF50P3 and ORF50P8 ( Fig. 2A, cycle 30 ). Recruitment of Egr-1 to the nonspecific ORF50NP region was not detectable in our experiments (data not shown). For negative controls, samples were IP with nonspecific (NS) IgG Abs and recruitment of Egr-1 to ORF50P was not observed ( Fig. 2A , cycle 30 on control gels). However, positive controls using specific Abs to histone proteins recovered ORF50P targets ( Fig. 2A) . These results help us confirm that Egr-1 binds to two separate domains on ORF50P, in vivo.