The tetratrico peptide repeat (TPR) is a degenerate 34-amino acid repeated motif that is widespread in evolutionL TPR proteins have been discovered in organisms as diverse as bacteria and humans, and in a variety of subcellular locations, including the nucleus, the cytoplasm and mitochondria. Processes involving TPR proteins include cellcycle control, transcription repression, stress response, protein kinase inhibition, mitochondrial and peroxisomal protein transport and neurogenesisL Therefore, there appears to be no common biochemical function connecting TPR-containing proteins. TPRs are frequently tandemly arrayed, although it is also common for single or double TPRs to be found separated from the arrays (Fig. In).

Comparison of TPRs from a variety of proteins reveals eight loosely conserved consensus residues (-W-LG-YAFAP-; see Fig. 2a and Refs 2, 3) within the 34 amino acids that define the motif. These residues are conserved in terms of their size, hydrophobicity and spacing. The high degree of sequence diversity observed in TPRs is consistent with the diversity of function o [TPR-containing proteins.