Carl Hirschie Johnson

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Cyanobacteria are the simplest organisms known to have a circadian clock. A circadian clock gene cluster kaiABC was cloned from the cyanobacterium Synechococcus. Nineteen clock mutations were mapped to the three kai genes. Promoter activities upstream of the kaiA and kaiB genes showed circadian rhythms of expression, and both kaiA and kaiBC messenger RNAs(More)
Cellular life emerged ∼3.7 billion years ago. With scant exception, terrestrial organisms have evolved under predictable daily cycles owing to the Earth's rotation. The advantage conferred on organisms that anticipate such environmental cycles has driven the evolution of endogenous circadian rhythms that tune internal physiology to external conditions. The(More)
Of the three defining properties of circadian rhythmicity--persisting free-running rhythm, temperature compensation, and entrainment--the last is often poorly understood by many chronobiologists. This paper gives an overview of entrainment. Where have we been? Where are we now? Whence should we be going? Particular emphasis is given to a discussion of the(More)
We describe a method for assaying protein interactions that offers some attractive advantages over previous assays. This method, called bioluminescence resonance energy transfer (BRET), uses a bioluminescent luciferase that is genetically fused to one candidate protein, and a green fluorescent protein mutant fused to another protein of interest.(More)
In some organisms longevity, growth, and developmental rate are improved when they are maintained on a light/dark cycle, the period of which "resonates" optimally with the period of the endogenous circadian clock. However, to our knowledge no studies have demonstrated that reproductive fitness per se is improved by resonance between the endogenous clock and(More)
To ascertain whether the circadian oscillator in the prokaryotic cyanobacterium Synechococcus PCC 7942 regulates the timing of cell division in rapidly growing cultures, we measured the rate of cell division, DNA content, cell size, and gene expression (monitored by luminescence of the PpsbAI::luxAB reporter) in cultures that were continuously diluted to(More)
We have used a luciferase reporter gene and continuous automated monitoring of bioluminescence to demonstrate unequivocally that cyanobacteria exhibit circadian behaviors that are fundamentally the same as circadian rhythms of eukaryotes. We also show that these rhythms can be studied by molecular methods in Synechococcus sp. PCC7942, a strain for which(More)
KaiC from Synechococcus elongatus PCC 7942 (KaiC) is an essential circadian clock protein in cyanobacteria. Previous sequence analyses suggested its inclusion in the RecADnaB superfamily. A characteristic of the proteins of this superfamily is that they form homohexameric complexes that bind DNA. We show here that KaiC also forms ring complexes with a(More)
The environment significantly influences the dynamic expression and assembly of all components encoded in the genome of an organism into functional biological networks. We have constructed a model for this process in Halobacterium salinarum NRC-1 through the data-driven discovery of regulatory and functional interrelationships among approximately 80% of its(More)
What are phase-response curves (PRCs)? How can they be measured? How should they be plotted? These questions and many other fascinating facets of PRCs are addressed in this review, including research topics in which phase-resetting data have provided crucial insights: entrainment, phototransduction, pacemaker mechanism, phase markers of the pacemaker, and(More)