Papers in the Biological Sciences
Date of this Version
2006
Citation
Journal of Bacteriology, Oct. 2006, p. 7141–7150, Vol. 188, No. 20
Abstract
Mercuric ion, Hg(II), inactivates generalized transcription in the crenarchaeote Sulfolobus solfataricus. Metal
challenge simultaneously derepresses transcription of mercuric reductase (merA) by interacting with the
archaeal transcription factor aMerR. Northern blot and primer extension analyses identified two additional
Hg(II)-inducible S. solfataricus genes, merH and merI (SSO2690), located on either side of merA. Transcription
initiating upstream of merH at promoter merHp was metal inducible and extended through merA and merI,
producing a merHAI transcript. Northern analysis of a merRA double mutant produced by linear DNA
recombination demonstrated merHp promoter activity was dependent on aMerR to overcome Hg(II) transcriptional
inhibition. Unexpectedly, in a merA disruption mutant, the merH transcript was transiently induced after
an initial period of Hg(II)-mediated transcription inhibition, indicating continued Hg(II) detoxification. Metal
challenge experiments using mutants created by markerless exchange verified the identity of the MerR binding
site as an inverted repeat (IR) sequence overlapping the transcription factor B binding recognition element of
merHp. The interaction of recombinant aMerR with merHp DNA, studied using electrophoretic mobility shift
analysis, demonstrated that complex formation was template specific and dependent on the presence of the IR
sequence but insensitive to Hg(II) addition and site-specific IR mutations that relieved in vivo merHp repression.
Despite containing a motif resembling a distant ArsR homolog, these results indicate aMerR remains
continuously DNA bound to protect and coordinate Hg(II)-responsive control over merHAI transcription. The
new genetic methods developed in this work will promote experimental studies on S. solfataricus and other
Crenarchaeota.
Comments
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