In the yeast S. cerevisiae 12 different members of a novel gene family of putative ATPases have been identified and characterised. Due to their similarities to TBP1, a human immunodeficiency tat binding protein, they have been designated the YTA family or yeast tat binding analogues. All share a region of high similarity of approximately 300 amino acids in length. Rpt5p or YTA1 ,is one of six ATPases of the 19S regulatory particle of the 26S proteasome involved in the degradation of ubiquitinated substrates.