<p>The HR1 repeat was first described as a three times repeated homology region of the N-terminal non-catalytic part of protein kinase PRK1(PKN) [<cite idref="PUB00006204"/>]. The first two of these repeats were later shown to bind the small G protein rho [<cite idref="PUB00006205"/>, <cite idref="PUB00006206"/>] known to activate PKN in its GTP-bound form. Similar rho-binding domains also occur in a number of other protein kinases and in the rho-binding proteins rhophilin and rhotekin. Recently, the structure of the N-terminal HR1 repeat complexed with RhoA has been determined by X-ray crystallography [<cite idref="PUB00006207"/>]. It forms an antiparallel coiled-coil fold termed an ACC finger.</p> HR1 rho-binding repeat