Circadian Rhythms of Gene Expression in Cyanobacteria

Texas A&M Research Foundation, College Station TX

Investigators

Abstract

The overall goal of this project is to understand the fundamental mechanisms by which a cell organizes a 24 h (circadian) biological clock. Central to models for animal and fungal circadian clock timing are feedback loops involving clock genes that negatively regulate their own expression. In the cyanobacterium Synechococcus elongatus (PCC 7942), the model organism for prokaryotic circadian biology, three genes (kaiA, kaiB, and kaiC) are required for circadian clock function. Data from mutants defective for, or that over-express, KaiA or KaiC suggest that KaiA is a positive activator, and KaiC a negative regulator, of the kaiBC promoter. However, other mutants of S. elongatus that change the relative expression of kaiA and kaiBC expression suggest that this parameter is not important for generating circadian rhythms. This project uses bioluminescent reporter genes to track circadian expression from S. elongatus strains in which kai gene expression has been manipulated to circumvent normal feedback loops. Changes in molecular events that are predicted to lie at the heart of the timing mechanism, such as the accumulation of each of the Kai proteins and their messages, and the phosphorylation state of the KaiC protein, will be monitored in mutant strains in which kai expression can be specifically manipulated. The project will reveal molecular parameters that contribute to the generation of a biological clock. The project will train postdoctoral and undergraduate students, and will generate sophisticated genetic tools for this and other cyanobacterial species, allowing a broader range of biological questions to be addressed.