The extremely halophilic archaeon Haloferax volcanii has two very different dihydrofolate reductases

Ron Ortenberg, Orit Rozenblatt-Rosen, Moshe Mevarech*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

34 Scopus citations


The gene encoding dihydrofolate reductase, hdrA, from the extremely halophilic archaeon Haloferax volcanii was previously isolated from a spontaneous trimethoprim-resistant mutant in a DNA sequence that had undergone amplification. Here, we show that deletion of hdrA did not affect growth in minimal medium and that the strain carrying the deletion remained sensitive to trimethoprim. A spontaneous trimethoprim-resistant colony was isolated in the hdrA deletion strain and found to possess a new DNA amplification. Sequencing of the amplification revealed a second, substantially different, dihydrofolate reductase gene, hdrB, which was found to be located immediately downstream of the thymidylate synthase gene, hts. The physiological role of hDHFR-1 and hDHFR-2 was determined by generating Haloferax volcanii strains in which each gene, hdrA or hdrB, or both genes were deleted. It was found that hdrB alone can support growth of Haloferax volcanii in minimal medium, whereas hdrA alone can support growth of Haloferax volcanii In minimal medium only when the medium is supplemented with thymidine. It was also shown that, in contrast to Escherichia coli, the ΔhdrA, ΔhdrB double deletion mutant is viable in the presence of a functional thymidylate synthase gene. The hdrB gene was overexpressed in Escherichia coli and the enzyme purified to homogeneity. The biochemical properties of the new enzyme (hDHFR-2) are markedly different from those of hDHFR-1. The use of the dihydrofolate reductase and thymidylate synthase genes as stable selectable markers is described.

Original languageEnglish
Pages (from-to)1493-1505
Number of pages13
JournalMolecular Microbiology
Issue number6
StatePublished - 2000


Dive into the research topics of 'The extremely halophilic archaeon Haloferax volcanii has two very different dihydrofolate reductases'. Together they form a unique fingerprint.

Cite this