Repressive Effect of the nef cDNA of Human Immunodeficiency Virus Type 1 on the Promoter Activity of the Viral Long Terminal Repeat

The nef gene product of human immunodeficiency virus type 1 (HIV‐1) has been implicated as a negative factor for viral replication and is suspected to play an important role in the maintenance of viral latency. However, there seems to be evidence both for and against the negative effect of nef gene product. In the present report, we reevaluated the function of the nef gene by means of transient CAT assays with two human T cell lines. In most of the experiments, carefully controlled triplicate studies were carried out. We observed that not only the nef‐expression plasmid, but also an effector plasmid containing the nef cDNA sequence in a reverse orientation, not expressing the Nef protein, showed a similar extent of repression of the HIV‐1 promoter activity. We also examined the repressive effect of the nef cDNA with deletion mutants of HIV‐1 long terminal repeat and heterologous promoters. The results led us to conclude that the apparent “repressor”‐like action of the nef cDNA itself could be explained by competition for certain transcription factors required for HIV‐1 gene expression by identical sequences also present in the nef cDNA.