IMPROVED ELECTROTRANSFORMATION OF HIGHLY DNA-RESTRICTIVE CORYNEBACTERIA WITH DNA EXTRACTED FROM STARVED ESCHERICHIA-COLI

Differences of up to 33 000-fold in electro-transformability of highly DNA restrictive corynebacteria are observed in the DNA of a shuttle p lasmid extracted from Escherichia coli hosts propagated in different n utritional conditions. Growth of the host in minimal medium increases plasmid transformability, whereas growth on rich media decreases it. I n the E. coli DH5 alpha. host, the starvation-dependent increase in DN A transformability is reverted by supplementing with methionine, an ob ligate S-adenosyl-methionine (SAM) precursor. This suggests that an E. coli nutritionally modulated SAM-dependent DNA-methyltransferase may be involved in this phenomenon.