Immunocytochemical localization of protein p27^BBP in human skin and invertebrate (Sepia officinalis) integument

The protein p27^BBP (alias eIF6) occurs in yeast and mammalian epithelial cells. It is essential for ribosome genesis and has also been implicated in the functionality of integrins and intermediate filaments. By immunoblot, we show that homogenized integument from Sepia officinalis (Cephalopoda, Mollusca) contains a protein with immunological properties that closely resemble those of p27^BBP. We also demonstrate, by immunogold electron microscopy with an indirect immunoreaction technique on ultrathin sections of human skin and Sepia integument, that p27^BBP is constantly present in both species in epithelial cells, fibroblasts, and muscle fibers. It is found in the vicinity of intermediate filaments, in nucleoli, along the internal wall of the nuclear membrane, and in association with desmosomes and hemidesmosomes and occasionally occurs extracellularly. Thus, the structure and function of p27^BBP seem to have been highly conserved throughout evolution; the protein appears to be essential in eukaryotic cells in which it interacts with several ultrastructural components of diverse function.