What archaea have to tell biologists

Photoreactivation of DNA by an archaeal nucleoprotein Sso7d

Sso7d is a chromosomal protein of hyperthermophilic Archaea. The crystal structure of Sso7d-d(GTAAT(I)UAC)(2) has been clarified at high resolution, showing that the protein binds in the minor groove of DNA, causing a sharp kink of approximately 60 degrees. Recently, we found that photoirradiation of Sso7d and 5-iodouracil-((I)U)-containing 5'-d(GTAAT(I)UAC)-3' efficiently induced the abstraction of hydrogen from the methyl group of T(5) at the kink. In the present study, we found that the photoreactivity of 5-bromouracil ((Br)U)-containing 5'-d(GTAAT(Br)UAC)-3' was enhanced in the presence of Sso7d. Using hypoxanthine (I)-containing 5'-d(ITAAT(Br)UAC)-3', we demonstrated that electron transfer occurs efficiently from Sso7d to DNA. Product analysis showed that Trp-24 of Sso7d, located at the surface of the DNA, is consumed to produce N'-formylkynurenine during photoirradiation, indicating that Trp-24 acts as an electron source. To explore the possibility of electron transfer between Sso7d and other DNA substrates, we examined the photochemical repair of the thymine dimer 5'-d(GTAAT<>TAC)-3' by Sso7d. Sso7d effectively repaired 5'-d(GTAAT<>TAC)-3' to 5'-d(GTAATTAC)-3' under irradiation conditions. During this reaction, Trp-24 was not oxidized significantly, indicating that the anion radical of the repaired TT sequence is oxidized by the cation radical of Trp-24, and that a so-called "circular electron transfer" mechanism is operating in this system.

Secreted euryarchaeal microhalocins kill hyperthermophilic crenarchaea

Few antibiotics targeting members of the archaeal domain are currently available for genetic studies. Since bacterial antibiotics are frequently directed against competing and related organisms, archaea by analogy might produce effective antiarchaeal antibiotics. Peptide antibiotic (halocin) preparations from euryarchaeal halophilic strains S8a, GN101, and TuA4 were found to be toxic for members of the hyperthermophilic crenarchaeal genus Sulfolobus. No toxicity was evident against representative bacteria or eukarya. Halocin S8 (strain S8a) and halocin R1 (strain GN101) preparations were cytostatic, while halocin A4 (strain TuA4) preparations were cytocidal. Subsequent studies focused on the use of halocin A4 preparations and Sulfolobus solfataricus. Strain TuA4 cell lysates were not toxic for S. solfataricus, and protease (but not nuclease) treatment of the halocin A4 preparation inactivated toxicity, indicating that the A4 toxic factor must be a secreted protein. Potassium chloride supplementation of the Sulfolobus assay medium potentiated toxicity, implicating use of a salt-dependent mechanism. The utility of halocin A4 preparations for genetic manipulation of S. solfataricus was assessed through the isolation of UV-induced resistant mutants. The mutants exhibited stable phenotypes and were placed into distinct classes based on their levels of resistance.