ComEA is a DNA receptor for transformation of competent Bacillus subtilis

Competent cells of Bacillus subtilis efficiently bind and internalize DNA. ComEA and the seven proteins encoded by the comG operon are required in viv o for the binding step. We show here that ComEA, a bitopic membrane protein , is itself capable of high-affinity DNA binding. A domain necessary for DN A binding is located at the C-terminus of ComEA. Proteins with similar 60-8 0 amino acid residue domains are widespread among bacteria and higher organ isms. ComEA shows a marked preference for double-stranded DNA and can bind to oligomers as small as 22 bp in length. DNA binding by ComEA exhibits no apparent base sequence specificity. Using a membrane vesicle DNA-binding as say system we show that in the absence of cell wall, ComEA is still require d for DNA binding, whereas the requirement for the ComG proteins is bypasse d. We conclude that the ComG proteins are needed in vivo to provide access of the binding domain of ComEA to exogenous DNA. Possible specific roles fo r the ComG proteins are discussed.