Robert Haselkorn
The University of Chicago
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Primary Section: 25, Plant Biology Secondary Section: 44, Microbial Biology Membership Type:
Member
(elected 1991)
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Research Interests
There are three separate research programs in my laboratory. The first is a comprehensive system for analysis of the chromosome of the photosynthetic bacterium, Rhodobacter capsulatus, which can do both photosynthesis and nitrogen fixation and can also grow on a wide variety of carbon sources. We have constructed a physical and genetic chromosome map using an ordered set of cloned DNA inserts in a cosmid vector. A defective transducing phage permits the construction of deletion strains simply and efficiently. We are determining the sequence of the chromosomal DNA cosmid by cosmid and making deletions as we go, in order to assign functions to the genes as they are found. The genome sequence has been completed. The metabolism of the bacterium is being reconstructed from the sequence. The second is the study of the differentiation of cells specialized for nitrogen fixation in the cyanobacterium Anabaena, which grows in filaments of several hundred cells. They all do green plant photosynthesis, evolving oxygen, as long as there is enough ammonia or nitrate in the growth medium. When such nitrogen sources are exhausted, the filaments differentiate heterocysts at regular intervals. These cells are anaerobic factories for nitrogen fixation, trading amino acids for carbohydrates with their vegetative cell neighbors. The differentiation process requires the orderly expression of perhaps 1,500 genes. We have used biochemical and genetic methods to isolate such genes and have in hand several hundred. Current work focuses on the regulatory genes that act early in the differentiation. The third project started with cyanobacteria but moved quickly to wheat. We have cloned genes from cyanobacteria encoding the enzyme acetyl CoA carboxylase (ACCase), which catalyzes the rate-limiting step in fatty acid biosynthesis. As such, it is the key to deposition of fats in seeds. Using the information gained from the cyanobacteria, we were able first to clone the ACCase cDNA from wheat and then to clone the corresponding genes. These are being studied with respect to tissue expression, developmental expression, and subcellular location of the enzyme. Recently, we found that the ACCase of Toxoplasma gondii is inhibited by herbicides specific for chloroplast ACCase of grasses. This opens the door to new drugs for parasite disease such as malaria.
