ELECTROTRANSFORMATION OF STREPTOCOCCUS-PNEUMONIAE - EVIDENCE FOR RESTRICTION OF THE DNA ON ENTRY

Electrotransformation is a method generally used in biotechnology to i ntroduce recombinant DNA into a wide range of bacteria. However the me chanism of DNA entry is poorly understood. We report that in Streptoco ccus pneumoniae, a naturally transformable species, electrotransformat ion efficiently introduces a plasmid replicon. DNA is strongly restric ted by the restriction-modification systems DpnI and DpnII which degra de methylated and nonmethylated DNA respectively at GATC sequences. Th is suggests that in electrotransformation double-strand DNA penetrates into these bacteria without a single-strand step in contrast to natur al transformation. Single-strand DNA by itself is able to electrotrans form very weakly and linearized double-stranded plasmid DNA yields bar ely detectable levels of transformants.