Mutations of the human cytomegalovirus immediate-early 2 protein defines regions and amino acid motifs important in transactivation of transcription from the HIV-1 LTR promoter.

The human cytomegalovirus (HCMV) immediate-early two (IE2) protein of 579 amino acids significantly activates expression from the human immunodeficiency virus (HIV) long terminal repeat (LTR) promoter. Using a proviral HIV-1 genome with a mutated tat gene we demonstrate that the IE2 protein effects an increase in the steady-state level of viral RNA similar to a level as from a wild-type proviral genome. The regions of the HCMV IE2 protein required for transactivation of the HIV-1 LTR promoter were analyzed by mutagenizing the IE2 gene and determining the activity of the mutant protein in human fibroblast cells. The region between amino acids 169 and 194 is required to transactivate the HIV-1 LTR promoter, although we have previously shown that this region is not required to activate a representative HCMV early promoter (C. L. Malone, et al., J. Virol. 64, 1498, (1990)). A region downstream of amino acid 290, which is required to activate a representative HCMV early promoter, is also required to activate the HIV-1 LTR promoter. Three types of mutations within this region were shown to greatly decrease IE2 activity: (1) amino acid substitutions of the cysteine or histidine residues in a putative zinc finger motif between amino acids 428 and 452; (2) substitution of the acidic charged residues between amino acids 558 and 561; (3) substitution of the two prolines at residues 556 and 557 immediately upstream of these acidic residues. Substitution of the other acidic residues near the carboxyl terminus also diminished transactivation by IE2. These data indicate that acidic amino acids and the secondary structure in the carboxyl end of the IE2 protein have an important role in transactivation of the HIV-1 LTR promoter. The other regions of the IE2 protein required for transactivation of the HIV-1 LTR are discussed.