Molecular cloning, sequencing, and expression of the heat-labile uracil-DNA glycosylase from a marine psychrophilic bacterium, strain BMTU3346

The gene encoding a heat-labile uracil-DNA glycosylase (UDG) from a psychrophilic, gram-positive marine strain (BMTU3346) has been cloned, sequenced, and expressed in Escherichia coli. The UDG is a cold-active enzyme with an apparent temperature optimum of 35°C and a half-life of 2 min at 40°C. The amino acid sequence shows an identity of 39.1%–46.2% to UDGs from mesophilic bacteria. The primary structure was examined for features that could be related to the thermolability of the enzyme. The amino acid sequence of the heat-labile UDG shows 22 differences with respect to the consensus sequence derived from bacterial UDGs. Features previously recognized in cold-active enzymes such as extended surface loops or a decrease in the number of arginine residues or proline residues in loops were not observed. Because dominant features that could be related to the thermolability of the UDG from BMTU3346 cannot be identified, more subtle modifications of the conformation seem to be responsible for its thermolability. Received: June 30, 1999 / Accepted: November 12, 1999