Papers in the Biological Sciences


Date of this Version



Journal of Bacteriology, Oct. 2006, p. 7141–7150, Vol. 188, No. 20


Copyright © 2006, American Society for Microbiology. All Rights Reserved.


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


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