In situ distribution of EcoRI methylase and restriction endonuclease in cells of Escherichia coli Bs 5

Abstract

Specific IgG antibodies were raised in rabbits against purified EcoRI methylase and restriction endonuclease. Post embedding labeling experiments, using the protein A-gold technique, were made with paraformaldehyde-glutaraldehyde fixed cells, embedded in Lowicryl K4M resin at low temperatures. Labeling with methylase-specific antibodies showed 60-70% of gold particles in the cytoplasm and 30-40% at the cell envelope, whereas the use of restriction enzyme-specific antibodies led to a distribution of 10-30% in the cytoplasm and 70-90% in the cell envelope. The results coincide with the proposed function of the enzymes: in the cytoplasm methylase protects the cells' own DNA from self-destruction, and the restriction endonuclease cuts foreign DNA when entering the cell.