Thermostable uracil-DNA glycosylase from Thermotoga maritima, a member of a novel class of DNA repair enzymes

Uracil-DNA glycosylase (UDG) is a ubiquitous enzyme found in eukaryotes and prokaryotes [1-3]. This enzyme removes uracil bases that are present in DN A as a result of either deamination of cytosine or misincorporation of dUMP instead of dTMP [4,5], and it is the primary activity in the DNA base exci sion repair pathway. Although UDG activities have been shown to be present in several thermophiles [6-8], no sequences have been found that are comple mentary to the Escherichia coli ung gene, which encodes UDG [9]. Here, we d escribe a UDG from the thermophile Thermotoga maritima. The T.maritima UDG gene has a low level of homology to the E.coli G-T/U mismatch-specific DNA glycosylase gene (mug). The expressed protein is capable of removing uracil from DNA containing either a U-A or a U-G base pair and is heat stable up to 75 degrees C. The enzyme is also active on single-stranded DNA containin g uracil. Analogous genes appear to be present in several prokaryotic organ isms, including thermophilic and mesophilic eubacteria as well as archaebac teria, the human-disease pathogens Treponema palladium and Rickettsia prowa zekii, and the extremely radioresistant organism Deinococcus radiodurans. T hese findings suggest that the T. maritima UDG is a member of a new class o f DNA repair enzymes. (C) Elsevier Science Ltd ISSN 0960-9822.