Related information:
|
Contact information
Recent publications
Curriculum vitae
Laboratory of Molecular Biology |
Biography:
Dr. Adhya received his Ph.D. from the University of Calcutta and also from
the University of Wisconsin. He was a Research Associate at University
of Rochester and Stanford University. He joined the Laboratory of Molecular
Biology in 1971. In 1994, Dr. Adhya was elected a member of the National
Academy of Sciences. Dr. Adhya has also been an AdjunctProfessor in the
Department of Genetics at George Washington University since 1987.
Research:
Virtually every adaptation and developmental process originate at the level
of gene regulation by transduction of extra- or intracellular signals.
Transcription is the major target of regulation of gene expression. Our
research interest covers modulation of transcription by DNA control elements
and regulatory proteins--for example, repressors, activators, terminators,
and antiterminators and their signal molecules. We have previously demonstrated
transcriptional regulation both at the level of initiation by activators
and repressors and at the level of elongation by terminators and antiterminators
in the IgalI operon which encodes enzymes of D-galactose
metabolism in IEscherichia coliI. Presumably because of the
amphibiotic nature of the biochemical pathway in carbon metabolism, the
operon shows a multitude of controls even at the level of transcription
initiation, and has been a paradigm system for studying control of transcription.
The operon is transcribed from two promoters which are subject to both
negative and positive control by at least four proteins, Gal repressor,
Gal isorepressor, cyclic AMP receptor protein, and bacterial histone like
protein, HU. The major highlight of our work in the past two years is the
revelation that GalR alone exerts control on the two promoters in a multivalent
way.
Regulation
by DNA looping. Synergistic repressor binding to two operators,
Synergistic repressor binding to two operators, OE and OI, encompassing the promoters P1 and P2, creates a DNA loop which inhibits transcription initiation from the gal promoters. A topologically closed loop of 11 helical turns, which is inflexible to torsional changes, disables the promoters by resisting DNA unwinding by RNA polymerase needed for open complex formation. Interaction between two proteins bound to different sites on DNA modulating the activity of the intervening segment toward other proteins may be a common mechanism of regulation in DNA-multiprotein complexes.
Requirement
of HU. Concurrent repression of the gal promoters by GalR needs
another factor, which has been purified and identified to be the bacterial
histone-like protein HU, and a supercoiled DNA template. Footprinting experiments
show that HU binds to gal DNA in a site-specific way, and HU binding
is entirely dependent upon binding of GalR to both OE
and OI. HU, in concert with GalR, forms a specific nucleoprotein
higher order complex containing a DNA loop. This way, while remaining sensitive
to inducer, HU deforms the promoter to make the latter inactive. The gal
repression system provides a model for studying how a "condensed" DNA becomes
available for transcription.
Atomic
force microscopic observation of DNA loop. We successfully applied
atomic force microscopy (AFM) imaging to visualize gal DNA loops
when complexed with GalR and HU. Supecoiling of DNA, which is critical
for GalR action, stabilizes the DNA loops by providing an energetically
favorable geometry of DNA.
Regulation
by DNA looping. Repressor binding to the upstream operator OE
alone, in the absence of DNA looping, represses one promoter P1
and activates the other P2. We have shown that both inhibition and
stimulation of transcription requires the presence of specific regions
of the alpha subunit of RNA polymerase. Our results suggest that Gal repressor
inhibits or stimulates transcription initiation by disabling or stimulating
RNA polymerase activity at a postbinding step by directly or indirectly
altering the specific domain of alpha to an unfavorable or to a more favorable
state, respectively.
A
new enzyme. We have discovered a new enzyme, aldose-1-epimerase, which
interconverts the two optical anomers of the inducer, D-galactose.
Inducer-repressor
interaction. By genetic and biochemical studies, we have identified
several residues in the Gal repressor which interact with the inducer.
Currently,
we are (1) studying the biochemical nature of the different nucleoprotein
complexes that control transcription initiation in gal; (2) investigating
the role of HU in repression; (3) detecting both genetically and biochemically
various protein-protein and DNA protein contacts in the different complexes;
and (4) identifying whether one or both of the optional anomers of the
D-galactose is the real inducer.
Recent
Publications:
|
Contact Information:
Laboratory
of Molecular Biology,
NCI,
NIH
Building
37, Room 2E16
37
CONVENT DR MSC 4255
BETHESDA
MD 20892-4255
|
