5-Hydroxymethyluracil-DNA glycosylase activity may be a differentiated mammalian function

To determine the prevalance of the repaire enzyme HMU-DNA hlycosylase we assayed its activity in whole cell extracts of several bacterial species, the eukaryotic yeast Saccharomyces cerevesiae, mammalian cell line and murine tissue. Enzyme activity was constitutively present in murine, hasmter and human cell lines. It was not inducible by exposing cells to oxidative stress from ionizing radiation or by incubating cells with the 2′-deoxynucleoside of HMU, HMdU. In murine tissue, enzyme activity was highest in brain and thymus. HMU-DNA glycosylase activity was not detectable in bacteria or yeast nor could activity be detected after exposure of cells to H₂O₂. These results suggest that, in contrast to other DNA-repair enzymes, HMU-DNA glycosylase is a differentiated function limited to higher eukaryotic organisms.