A HUMAN MITOCHONDRIAL ATP-DEPENDENT PROTEASE THAT IS HIGHLY HOMOLOGOUS TO BACTERIAL LON PROTEASE

We have cloned a human ATP-dependent protease that is highly homologou s to members of the bacterial Lon protease family. The cloned gene enc odes a protein of 963 amino acids with a calculated molecular mass of 106 kDa, slightly higher than that observed by Western blotting the pr otein from human tissues and cell lines (100 kDa). A single species of mRNA was found for this Lon protease in all human tissues examined. T he protease is encoded in the nucleus, and the amino-terminal portion of the protein sequence contains a potential mitochondrial targeting p resequence. Immunofluorescence microscopy suggested a predominantly mi tochondrial localization for the Lon protease in cultured human cells. A truncated LON gene, in which translation was initiated at Met118 of the coding sequence, was expressed in Escherichia coli and produced a protease that degraded alpha-casein in vitro in an ATP-dependent mann er and had other properties similar to E. coli Lon protease.