A LEUCONOSTOC LACTIS PROTEIN WITH HOMOLOGY TO RIBOSOMAL-PROTEIN S1 SHARES COMMON EPITOPES AND COMMON DNA-BINDING PROPERTIES WITH A MAMMALIAN DNA-BINDING NUCLEAR FACTOR

A mouse testis cDNA expression library (Clontech) was screened with a synthetic oligonucleotide ligand containing CT-rich motifs derived fro m the rat skeletal muscle actin gene promoter. These motifs bind nucle ar proteins, and seem to be involved in the regulation of the gene. An alysis of isolated clones, which expressed proteins that specifically bind the oligonucleotide, indicated that they were derived from a sing le gene. This gene was identified as a contaminant of bacterial origin (Leuconostoc lactis). The cloned gene from L. lactis encodes a protei n with significant homology to bacterial ribosomal protein S1, which w e designated LrpS1-L. Band shift analysis and competition experiments indicated that both the bacterial protein and a mouse nuclear protein specifically bind to the same CT-rich motif of the skeletal muscle act in promoter. Furthermore, antibodies against the recombinant bacterial protein interfered with the formation of complex between the CT-rich element and the mouse nuclear protein. These results indicate that the bacterial LrpS1-L protein and the mammalian protein bind the same CT- rich motif and share common antigenic epitopes.