The DNA transporter ComEC has metal-dependent nuclease activity that is important for natural transformation

In the process of natural transformation bacteria import extracellular DNA molecules for integration into their genome. One strand of the incoming DNA molecule is degraded, whereas the remaining strand is transported across the cytoplasmic membrane. The DNA transport channel is provided by the protein ComEC. Many ComEC proteins have an extracellular C-terminal domain (CTD) with homology to the metallo-beta-lactamase fold. Here we show that this CTD binds Mn2+ ions and exhibits Mn2+-dependent phosphodiesterase and nuclease activities. Inactivation of the enzymatic activity of the CTD severely inhibits natural transformation in Bacillus subtilis. These data suggest that the ComEC CTD is a nuclease responsible for degrading the nontransforming DNA strand during natural transformation and that this process is important for efficient DNA import.

Automated summary

During natural transformation, bacteria import extracellular DNA molecules into their genome using the protein ComEC. The C-terminal domain (CTD) of ComEC binds Mn2+ ions and exhibits Mn2+-dependent phosphodiesterase and nuclease activities. Inactivation of the CTD's enzymatic activity severely inhibits natural transformation in Bacillus subtilis.