Isolation and characterization of IPP, a novel human gene encoding an actin-binding, kelch-like protein

The kelch family of proteins is defined by a 50 amino-acid repeat that has been shown to associate with actin. Here we describe the cloning and initial characterization of IPP, a novel human gene that predicts a kelch family protein homologous to the mouse Ipp gene, a previously described kelch family member. A 3 kb IPP cDNA clone was isolated from a human placenta library using a probe derived from Ipp. Restriction mapping and Southern blot analysis show that IPP comprises eight exons spanning more than 47 kb of genomic DNA. Fluorescence in situ hybridization maps the gene to chromosome 1p32-1p34. Northern blot analysis reveals transcripts of 1.4, 2.2, 5.0, and 7.3 kb. The 1.4 and 2.2 kb messages are found exclusively in testis, while the 5.0 and 7.3 kb messages are expressed at varying levels in ovary, placenta, small intestine, spleen, testis, and thymus. The IPP cDNA clone contains a 1752 bp open reading frame that predicts a 584 amino-acid, 66 kDa protein. Sequence analysis indicates an N-terminal POZ protein-protein interaction domain and a C-terminal kelch repeat domain consisting of six tandemly arranged repeats. Cosedimentation assays performed with these domains expressed as glutathione S-transferase fusion proteins demonstrate an actin-binding activity mediated specifically by the kelch repeat domain of IPP. (C) 1999 Published by Elsevier Science B.V. All rights reserved.