A reporter cell line with stably integrated retroviral promoter-luciferase construct was transfected with an expression vector for a cellular protein. The protein seems to regulate the activation of the retroviral promoter as analyzed by luciferase activity assay. Which one of the following techniques will you use to show in vivo recruitment of the cellular protein on the integrated retroviral promoter?

a. Electrophoretic mobility shift assay

b. RNAse protection assay

c. DNAse hypersensitivity assay

d. Chromatin immunoprecipitation assay