Structure and expression of the equine infectious anemia virus transcriptional trans-activator (tat).

Equine infectious anemia virus (EIAV) encodes a tat gene which is closely related to the trans-activators encoded by the human and simian immunodeficiency viruses. Nucleotide sequence analysis of EIAV cDNA clones revealed that the tat message is composed of three exons; the first two encode tat and the third may encode rev.. Interestingly, EIAV tat translation is initiated at a non-AUG codon in the first exon of the message, perhaps allowing an additional level of gene regulation. The deduced amino acid sequence of EIAV tat, combined with functional analyses of tat cDNAs in transfected cells, have provided some unique insights into the domain structure of this protein. EIAV Tat has a C-terminal basic domain, a highly conserved 16 amino acid core domain, but not the cysteine-rich region, that is present in the primate immunodeficiency virus Tat proteins. Thus EIAV encodes a relatively simple version of this kind of trans-activator.