Diverse eukaryotes, and at least one group of prokaryotes—cyanobacteria—use a circadian (24 h) clock to control physiological events and gene expression. S. elongatus shows a circadian rhythm of bioluminescence when it is transformed with a reporter gene that encodes the luciferase of a bioluminescent marine bacterium or firefly. We are using this reporter system to identify components of circadian system. A group of interacting proteins, KaiA, KaiB, and KaiC are at the heart of the cyanobacterial clock, and kinases help to set the clock and transmit temporal information from it to the genes it regulates. Our goal is to understand the basic mechanism of timekeeping and how the clock becomes synchronized with the environment and controls cellular processes.
We are identifying all of the genes in the S. elongatus genome that contribute to circadian rhythms by creating a mutation in each gene and assaying each mutant for circadian phenotypes. This project uses transposon insertions into cosmids and plasmids that contain pieces of S. elongatus DNA; each clone that carries a transposon insertion can be used for recombination into the S. elongatus genome to produce a gene "knockout."
Because cyanobacteria grow photosynthetically using water and CO2 and are easy to manipulate genetically, they are attractive organisms for the production of molecules that have industrial applications. One such application is the production of biofuels as a supplementation of or eventual replacement of petroleum fuels. We are using the powerful genetic tools that have been developed for S. elongatus to explore the production of biofuels in cyanobacteria.
Susan Golden received a B.A. (1978) in Biology from Mississippi University for Women and a Ph.D. (1983) in Genetics from the University of Missouri. After postdoctoral research at the University of Chicago, she joined the faculty of Biology at Texas A&M University (1986), where she was promoted to Distinguished Professor in 2003. She joined the Division of Biological Sciences at UCSD in 2008.
During her graduate work she developed genetic tools for the cyanobacterium Synechococcus elongatus (PCC 7942), the first cyanobacterium shown to be subject to genetic transformation. This led to work on regulation of light-responsive photosynthesis gene expression in this organism during her postdoctoral research and at Texas A&M. In the early 1990s she began a collaborative project with C.H. Johnson (Vanderbilt University) and T. Kondo (Nagoya University) that demonstrated circadian rhythms of gene expression in S. elongatus, which is currently the only model organism for a prokaryotic circadian clock. The molecular basis of timekeeping in S. elongatus is now a major focus of her lab. Susan is a member of the Faculty of 1000 Biology, a Fellow of the American Academy of Microbiology, and a Member of the National Academy of Sciences.