Circadian Rhythms and the Transcriptional Feedback Loop (Nobel Lecture)*

Area of Science:

• * Chronobiology
• * Evolutionary biology
• * Molecular biology

Background:

• * Circadian rhythms are endogenous daily biological cycles influencing physiological processes in most life forms.
• * These rhythms are observed across diverse taxa, including animals, plants, and cyanobacteria.
• * Understanding the evolutionary origins of circadian clocks is crucial for comprehending their fundamental importance.

Purpose of the Study:

• * To investigate the evolutionary origins and molecular basis of circadian clocks in different organisms.
• * To compare the molecular machinery of circadian clocks across animals, plants, and cyanobacteria.
• * To determine if circadian rhythms evolved independently in different life forms.

Main Methods:

• * Comparative analysis of clock protein structures and sequences.
• * Bioinformatic analysis of genes involved in circadian rhythmicity.
• * Literature review of existing studies on circadian clocks in various taxa.

Main Results:

• * Circadian clocks are widespread, found in animals, plants, and photosynthetic cyanobacteria.
• * Molecular mechanisms of cyanobacterial and plant clocks are distinct from animal clocks, with no significant protein homology.
• * The structural and sequence divergence indicates independent evolutionary trajectories for these biological clocks.

Conclusions:

• * Circadian rhythms have likely evolved multiple times independently throughout evolutionary history.
• * The lack of homology underscores the convergent evolution of daily biological timing mechanisms.
• * The repeated emergence of circadian regulation highlights its significant adaptive advantage for life on Earth.