Postdoctoral position

Mon Jan 8 20:52:12 EST 1996

A postdoctoral position is available for a person interested in 
molecular and biochemical aspects of the transduction of blue light 
signals in phototropism. Interested individuals should send inquiries 
and cv's and arrange to have three letters of reference sent to:

Winslow R. Briggs 
Department of Plant Biology
Carnegie Iinstitution of Washington
Stanford, CA 94305 

The position is available immediately.

An abstract of the research planned follows:

IN Arabidopsis thaliana)

We have been studying a plant plasma membrane protein that becomes
heavily phosphorylated on irradiation with blue light either in vivo
or in vitro. Both physiological and genetic evidence implicate this
protein in an early step in the signal transduction pathway for
phototropism, and there is evidence that it may itself be the
photoreceptor. We have recently isolated a number of severe
phototropism mutants in Arabidopsis thaliana designated nph for
non-phototropic hypocotyl. They fall into four complementation
groups, nph1-4.All five alleles of the first group, nph1, are
deficient in or lack the phosphoprotein but show normal
gravitropism, and it is the NPH1 gene that is focal point for this
proposal. Our working hypothesis is that NPH1 is the gene that
encodes the phosphoprotein. As the weakest allele (nph1-2) shows
altered spectral sensitivity for phototropism, NPH1 may itself be
the photoreceptor. Since the three strong alleles, nph1-1, nph1-3,
and nph1-4, lack all known phototropic responses in A. thaliana, the
phosphoprotein, NPH1, appears essential for all phototropic signal
transduction pathways in this plant. We have used a combination of
molecular and genetic techniques that we believe will allow us to
clone the NPH1 gene before the proposed starting date for this

	Once the putative NPH1 gene is cloned, we will first attempt to
rescue nph1 mutant alleles by transformation. If the results
indicate that we have indeed complemented the mutants, we plan to
use the cloned gene a) to study the effect of overexpression on
phototropism physiology and the physiology of a number of other
other blue light-sensitive phenomena such as hypocotyl elongation,
stomatal opening, circadian rhythm phase, chloroplast movement,
etc.; b) as a probe to clone and characterize the other mutant
alleles of NPH1; c) as a probe to clone and characterize the
homologous gene in other species and search for related genes in
Arabidopsis; d) to investigate NPH1 expression at the mRNA level in
different tissues, during development, and under different
light/dark conditions; e) to obtain the deduced amino acid sequence
for the NPH1 protein to look for homologies in other proteins--e. g.
flavoproteins, DNA photolyases and photolyase-like proteins, to look
for possible functional domains for protein-protein interaction,
chromophore binding, membrane association, etc. We will also look
for reaction partners with NPH1 by using cross-linking reagents,
two-hybrid complementation, etc. to investigate further elements in
the signal transduction pathway. 

	We also plan to construct an expression system with the following
objectives: a) to do further biochemical characterization of the
protein; b) to study potential chromophore association; c) to
generate monoclonal and polyclonal antibodies; d) to investigate
possible mechanisms for photoactivation of phosphorylation of the
expressed protein if it shows photoactivity; and e) if possible to
use it as a starting point for site-directed mutagenesis studies. 

	Once we have antibodies, we plan to investigate a) protein
distribution in various tissues, during development; b) the fate of
the protein following phosphorylation; c) the behavior of the protein
in light-grown plants; and d) the possible occurrence of the protein
in other groups of lower plants and fungi. We will also use
monoclonal antibodies e) to do epitope mapping and look for
structural domains conserved between several species. 

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