Many studies showed that the p300/CBP coactivator is limiting. Here we review three studies that showed howtranscription complexes formed on viral cis-regulator elements compete with cellular transcription complexesby sequestrating the p300/CBP coactivator. According to the microcompetition model, this sequestering cancause disease. We use the microcompetition model to explain how a specific type of sequestering, caused by alatent virus that has an active cis-regulatory element in its promoter/enhancer that binds the transcriptioncomplex p300/CBP.GABP can cause diseases such as cancer, atherosclerosis, diabetes, and certain autoimmunediseases.