Cloning of Xenopus RCC1 cDNA, a homolog of the human RCC1 gene: complementation of tsBN2 mutation and identification of the product.

We isolated a cDNA clone from Xenopus cDNA libraries for the homolog of the human RCC1 gene, which is considered to be a regulator for the onset of chromosome condensation. The cloned Xenopus RCC1 cDNA encoded a protein of 424 amino acids which had the same seven homologous repeated domains of about 60 amino acids as found in human RCC1 cDNA. The overall identity of amino acid sequence between the human and Xenopus RCC1 protein was 76%. Specifically, in the repeated domain the amino acid sequence was highly conserved between both species. The identity of amino acids in this region was 82%. In the N-terminal region, albeit the overall identity was low (35%), some positively charged amino acids were conserved. The transcript for Xenopus RCC1 gene with the length of 2.2-kb was detected in both Xenopus oocytes and cultured somatic cells, A6. The antibody prepared against Xenopus RCC1 protein produced in E. coli recognized 45 and 46 kDa proteins not only in Xenopus oocytes and A6 cells, but also in human and hamster cells. Xenopus RCC1 cDNA complemented the tsBN2 mutation, depending on the amount of its product in transformants. Thus, the RCC1 protein was suggested to regulate the onset of chromosome condensation in the eukaryote from amphibian to mammalian cells.