Ubiquicidin, a novel murine microbicidal protein present in the cytosolic fraction of macrophages

Previously we have identified and characterized three murine microbicidal p roteins purified from the granule fraction of cells from the murine macroph age cell Line RAW264.7. During these studies evidence was obtained for the presence of an additional antimicrobial protein in the cytosolic fraction o f RAW264.7 cells that had been activated with interferon-gamma (IFN-gamma), In this study we have purified this protein, designated ubiquicidin, to ap parent homogeneity and demonstrated that it is a cationic, small (M-r 6654) protein, Ubiquicidin displayed marked antimicrobial activity against Liste ria monocytogenes and Salmonella typhimurium, Using a gel overlay procedure evidence was obtained that the protein also displays activity against Esch erichia coli, Staphylococcus aureus, and an avirulent strain of Yersinia en terocolitica. Aminoterminal amino acid sequencing and mass spectrometry ana lysis of purified ubiquicidin indicated that it is most likely identical to the ribosomal protein S30, This protein is produced by posttranslational p rocessing of the Fau protein, a 133-amino-acid fusion protein consisting of S30 linked to an unusual peptide with significant homology to ubiquitin. T he fau gene has been reported to be expressed in a variety of tissues in hu mans and various animal species. The presence of ubiquicidin in the cytosol of macrophages may serve to restrict the intracellular growth of microorga nisms. In addition, because macrophage disintegration will likely lead to r elease of ubiquicidin into the extracellular environment, it may contribute to host defense after macrophage death.