Transformasomes: specialized membranous structures that protect DNA during Haemophilus transformation

Abstract

The mechanism by which Haemophilus protects donor DNA from cellular restriction and degradative enzymes during transformation is unclear. In this report, we demonstrate that donor DNA enters Haemophilus influenzae through specialized membranous extensions, which we have termed "transformasomes." DNA within transformasomes is in a protected state--resistant to external DNase and cellular restriction enzymes, although remaining unmodified and double-stranded. The ability of donor DNA to exit from transformasomes is dependent on its topological conformation. Circular DNA remains intact within transformasomes, while linear DNA rapidly exits and undergoes homologous recombination. Protected donor DNA can be preferentially removed from the surface of competent cells by extraction with organic solvents. Structurally intact transformasomes containing donor DNA could be partitioned into the organic layer and can be further purified by density centrifugation.