Trans-activator (Tat) proteins regulate the transcription of lentivira
l DNA in the host cell genome. These RNA binding proteins participate
in the life cycle of all known lentiviruses, such as the human immunod
eficiency viruses (HIV) or the equine infectious anemia virus (EIAV).
The consensus RNA binding motifs [the trans-activation responsive elem
ent (TAR)] of HIV-1 as well as EIAV Tat proteins are well characterize
d. The structure of the 75-amino acid EIAV Tat protein in solution was
determined by two- and three-dimensional nuclear magnetic resonance m
ethods and molecular dynamics calculations. The protein structure exhi
bits a well-defined hydrophobic core of 15 amino acids that serves as
a scaffold for two flexible domains corresponding to the NH2- and COOH
-terminal regions. The core region is a strictly conserved sequence re
gion among the known Tat proteins. The structural data can be used to
explain several of the observed features of Tat proteins.