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Abstract:
In Methanobacterium thermoautotrophicum, the fmdECB operon encoding the
molybdenum formylmethanofuran dehydrogenase is directly preceded by an
open reading frame tfx predicted to encode a DNA binding protein. The
16.1 kDa protein has an N-terminal basic domain with a helix-turn-helix
motif for DNA binding and a C-terminal acidic domain possibly for
transcriptional activation. We report here on the DNA binding properties
of the Tfx protein heterologously overproduced in Escherichia coli. Tfx
was found to bind specifically to a DNA sequence downstream of the
promoter of the fmdECB operon, as shown by electrophoretic mobility
shift assays and DNase I footprint analysis. Northern blot
hybridizations revealed that transcription of tfx is repressed during
the growth of M. thermoautotrophicum in the presence of tungstate. Based
on its structure and properties, the DNA binding protein Tfx is proposed
to be a transcriptional regulator composed of a basic DNA binding domain
and an acidic activation domain.
