M. Skorvaga et al., THERMOSTABLE ARCHAEAL O-6-ALKYLGUANINE-DNA ALKYLTRANSFERASES, Proceedings of the National Academy of Sciences of the United Statesof America, 95(12), 1998, pp. 6711-6715
Archaea represent some of the most ancient organisms on earth, and the
y have relatively uncharacterized DNA repair processes. We now show, u
sing an in vitro assay, that extracts of two Crenarchaeota (Sulfolobus
acidocaldarius and Pyrobaculum islandicum) and two Euryarchaeota (Pyr
ococcus furiosus and Thermococcus litoralis) contain the DNA repair pr
otein O-6-alkylguanine-DNA alkyltransferase (ATase). The ATase activit
ies found in the archaea were extremely thermostable, with half-lives
at 80 degrees C ranging from 0.5 hr (S, acidocalrlarius) to 13 hr (T.
liroralis), The temperature optima of the four proteins ranged from ap
proximate to 75 to approximate to 100 degrees C, although activity was
seen at 37 degrees C, the temperature optimum of the Escherichia coil
and human ATases. In all cases, preincubaton of extracts with a short
oligonucleotide containing a single O-6-methylguanine residue caused
essentially complete loss of ATase activity, suggesting that the alkyl
phosphotriester-DNA alkyltransferase activity seen in some prokaryotes
is not present in Archaea. The ATase from Pyrobaculum islandicum had
an apparent molecular mass of 15 kDa, making it the smallest of these
proteins so far described. In higher organisms, ATase is responsible f
or the repair of toxic and mutagenic O-6-alkylguanine lesions in alkyl
ated DNA, The presence of ATase in these primitive organisms therefore
suggests that endogenous or exogenous exposure to agents that generat
e appropriate substrates in DNA may be an early event in evolution.