Parallel analyses of DNA copy number and mRNA expression level by using microarray measurements have been successfully applied for genome-wide screening of proto-oncogenes and tumor suppressor genes. The uncharacterized KIAA0456 cDNA was reported amplified and overexpressed in human breast cancer cell lines UACC812 and ZR-75-1. Here, we characterized the gene corresponding to KIAA0456 cDNA by using bioinformatics. KIAA0456 cDNA was found derived from the FNBP2 gene, consisting of 22 exons. FNBP2 gene was linked to IKBKE and NORE1 genes on human chromosome 1q32.1. FNBP2 mRNA was expressed in melanoma, germ cell tumors, chondrosarcoma and retinoblastoma. ARHGAP13/SRGAP1, ARHGAP14/SRGAP2 and ARHGAP4 cDNAs were homologous to FNBP2/KIAA0456 cDNA. KIAA1304 cDNA was a splicing variant derived from the ARHGAP13 gene, and the nucleotide sequence of representative ARHGAP13 cDNA was determined by assembling EST BU520980 and KIAA1304 cDNA. FNBP2 (1071 aa), ARHGAP13 (1062 aa), ARHGAP14 (1099 aa) and ARHGAP4 (946 aa) constitute the FNBP2 family characterized by FCH, RhoGAP and SH3 domains. The region corresponding to codon 227-345 of FNBP2 was conserved among FNBP2 family proteins as well as FNBP1 and TRIP10 proteins. Because FNBP2 and FNBP1 are formin-binding proteins, the region corresponding to codon 227-345 of FNBP2 was designated FNBP2-FNBP1 homologous (FBH) domain. FNBP2 family proteins consist of FCH, FBH, RhoGAP and SH3 domains, while FNBP1 family proteins (FNBP1 and TRIP10) consist of FCH, FBH and SH3 domains. This is the first report on comprehensive characterization of FNBP2 gene as well as on identification of the FBH domain.

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