We identified in the EST database routine and human sequences similar, but not identical, to the members of the PC3/BTG/TOB family of cell cycle inhibitors. A conserved domain (aa 50-68) of the PC3 protein, the prototype member of the family, was used as a query. That domain has been shown by us to be necessary for the antiproliferative activity of PC3. A routine EST clone and a highly homologous human EST clone, containing the entire ORF, were chosen for sequencing. Comparison to databases and a phylogenetic tree analysis indicated thai these EST clones are the mouse and human homologues of a gene that represents a novel member of the PC3/BTG/TOB family. This gene, named PC3B, is endowed with marked antiproliferative activity, being able to induce G1 arrest, and is highly expressed in testis, in oocyte, and in preimplantation embryos. Analysis of its expression during routine development indicated a specific localization in the olfactory epithelium at midgestation, suggesting that PC3B might be involved in the differentiation of this neuronal structure. Human PC3B mapped to chromosome 11q23, as indicated by radiation hybrid analysis. (C) 2000 Academic Press.
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