Does the human immunodeficiency virus Tat trans-activator contain a discrete activation domain?
Human immunodeficiency virus type 1 (HIV-1) encodes a transcriptional trans-activator, termed Tat, that is absolutely required for viral replication in vitro. By analogy to other known transcription factors, it has been suggested that the HIV-1 Tat protein may contain discrete protein domains that determine sequence specificity and transcriptional activation potential. Here, we report the use of site-directed mutagenesis to examine the functional significance of two candidate activation domains within Tat. A 12 amino acid sequence adjacent to the N-terminus of the Tat protein, which includes a proposed acidic amphipathic alpha-helix activation motif, was found to contribute to, but be dispensable for, Tat function in vivo. In contrast, the integrity of a second potential Tat activation motif, centered on a lysine residue at position 41, was found to be essential for Tat function. However, Tat proteins mutated in this area displayed a fully recessive negative phenotype. Therefore, neither of these two regions of the Tat protein appear to be discrete activation domains. We conclude that previous attempts to categorize Tat as a modular transcription factor have not succeeded and suggest that the functional organization of this complex trans-activator remains to be defined.
Tiley
L S
LS
Department of Microbiology and Immunology, Duke University Medical Center, Durham, North Carolina 27710.
Brown
P H
PH
Cullen
B R
BR
D000595:Amino Acid Sequence; D002478:Cells, Cultured; D015696:Gene Products, tat / Q000235:genetics*; D015497:HIV-1 / Q000235:genetics*; D006801:Humans; D008969:Molecular Sequence Data; D009154:Mutation; D012091:Repetitive Sequences, Nucleic Acid; D015534:Trans-Activators / Q000235:genetics*; D015533:Transcriptional Activation; D054322:tat Gene Products, Human Immunodeficiency Virus
D015696:Gene Products, tat; D015534:Trans-Activators; D054322:tat Gene Products, Human Immunodeficiency Virus