Student Research Project
Regulation of cyanobacterial genes by light and the circadian clock
Students
Matthew Gordon
Major: Zoology
Future Plans: Graduate school or industry research
Casey Downs
Major: Biochemistry and Genetics
Future Plans: Graduate school
Professor
Susan S. Golden, Associate Professor, Department of Biology, Texas A&M University, College Station
My laboratory uses cyanobacteria to study two ways that cells coordinate their metabolisms with what is going on in the environment. The first is the regulation of photosynthesis genes by light intensity, and the other is the control of gene expression by a circadian clock. Cyanobacteria are eubacteria that carry out photosynthesis in fundamentally the same way as plant chloroplasts. We have found that they dramatically alter the expression of certain photosynthesis genes in response to changes in light intensity. The outcome is that the cell makes the right amount and the right kind of photosynthesis protein to match the demand for that component under the prevailing conditions. We are trying to learn how the cell senses the change in light intensity and what molecules carry the light signals to the genes. Our work on the circadian clock is aimed at figuring out the timekeeping mechanism. The chemical nature of the biological clock is not known for any organism, and a bacterium that possesses a clock is the simplest available system for revealing the pacemaker.
For both projects, we follow the expression of "reporter genes" in which the regulatory signals of light- or clock-controlled genes are hooked up to the coding regions of genes whose expression is easy to measure. One of our favorite reporters is the luxAB gene set, whose product is a light-producing enzyme. Cells that carry luxAB glow as a function of the gene whose regulatory signals are being measured. A sensitive video camera can record the light production. When luxAB is fused to a clock-controlled gene, light production rises and falls in a daily cycle. For measurement of light-regulated genes, we can see that the amount of light produced by the cells depends on how much light the cells absorbed before the measurement.
We use strains that carry the reporter gene inserted into their chromosome and isolate mutants that no longer regulate luxAB expression properly. In the photosynthesis project, this may be a mutant that fails to respond to changes in light intensity. A clock mutant might show a rhythm of light production that operates on a 20 h cycle instead of a 24 h cycle. To find the mutated gene, we add genes back and pick out the colonies in which the reporter gene is once again regulated properly. The gene that fixed the problem should be the one that was altered in the mutant. In this way, we are able to identify genes that code for components of the signaling pathway, or parts of the clock. So far we have identified regions of the photosynthesis genes that receive the light signals, but we are still looking for the molecules that interact with them. We have several mutants in circadian clock function, and now we are trying to find the genes that are affected in each. |
2002 McGraw-Hill Higher Education