Upstream Stimulatory Factor (USF) and CCAAT/Enhancer Binding Protein δ (C/EBPδ) Compete for overlapping Sites in the Negative Regulatory Region of the HIV-1 LTR

Abstract

Human immunodeficiency virus type 1 (HIV-1) is a human retrovirus and the causative agent of the acquired immunodeficiency syndrome. Genetic analysis has revealed that the HIV-1 LTR contains a potential negative regulatory element (NRE) with an E box, the recognition sequence for the helix-loop-helix (HLH) family of transcription factors. Furthermore, the upstream stimulatory factor (USF) has been implicated as a negative regulator of HIV-1 expression. Here, we report that the NRE is a composite element and that both C/EBPδ and USF can specifically bind to the NRE. The recognition sequence for C/EBPδ overlaps with the E box in the NRE of HIV-1. Competition experiments showed that either USF or C/EBPδ binds to this NRE but not both together.