Variants of the HIV-1 Tat protein exhibiting higher transcriptional activation and stronger P-TEFb binding than wild-type Tat are provided. In addition variants that can inhibit transcription activation by wild-type Tat are provided. Nucleic acid sequences encoding these variants, vectors and host cells for expression of these variants, and antibodies raised against these variants are also provided. In addition, methods for use of these variants and compositions containing these variants as research tools, as diagnostic tools and in the treatment of viral infections are provided.