Canavanine-induced fast-sedimenting complexes with Escherichia coli DNA and bacteriophage T4 DNA

Arginine-requiring strains of Escherichia coli grown with l-canavanine formed a heavy canavanyl-protein complex with about 60% of the cell DNA as shown by zonal sedimentation in sucrose-EDTA gradients. DNA, made both during and prior to growth in canavanine, bound to this heavy complex, presumed to include cell membrane. The time course of DNA binding followed the deposition of canavanyl-protein into the complex. Both formation of the complex and canavanine death occurred in the presence or absence of DNA synthesis without apparent coordination with the DNA replication cycle. Various treatments of lysates prior to zonal sedimentation suggested that protein and perhaps lipid components were essential for binding of DNA to the heavy complex. Parental DNA of ³²P-labeled bacteriophage T4 was bound to a fast-sedimentating fraction of arginine-starved E. coli dependent upon protein synthesis during infection. Cells pregrown with l-canavanine formed the heavy ³²P-T4 DNA complex in the absence of protein synthesis. A canavanine-resistant mutant grown with canavanine formed a heavy protein fraction that did not complex with cellular DNA, and binding of T4 DNA required protein synthesis during infection of canavanine-grown cells. The results suggest that canavanine death of E. coli is caused by the incorporation of canavanine into a heavy membrane-protein that binds DNA abnormally.