# The Linchpin that Joins the Circadian Oscillator to Clock Output

> **NIH NIH R01** · UNIVERSITY OF CALIFORNIA, MERCED · 2020 · $327,688

## Abstract

PROJECT SUMMARY/ABSTRACT
!
Numerous life forms including bacteria, fungi, plants, and animals involuntarily regulate their
metabolism, physiology, and behavior in anticipation of sunrise and sunset. These circadian
rhythms arise from endogenous molecular timekeeping systems, called circadian clocks, which
generate waves of assembly and disassembly of clock components. Unknown are the temporal
and causal relationships between these transitory events, and how they are important to clock
function. The objective of the LiWang lab is to elucidate the dynamic mechanism by which these
waves are produced by and transmitted from the circadian oscillator, through clock-output
pathways, to transcription factor-DNA binding rhythms. The approach is to carry out real-time
measurements in vitro on the cyanobacterial circadian clock, reconstituted in its entirety (six
proteins and DNA) outside the milieu of live cells. Despite the availability of a near-complete set
of high-resolution structures of cyanobacterial clock protein complexes (manuscript under review
at Science, submitted on 06/04/16), the dynamic mechanism of this system remains obscure.
Thus, the LiWang lab is conducting real-time experiments on reconstituted cyanobacterial
circadian clock reactions to unravel the dynamic timekeeping mechanism of this system. In aim 1,
the LiWang lab will elucidate the temporal and causal relationships between transitory interaction
events at the molecular level, using real-time nuclear magnetic resonance spectroscopy (NMR).
Time signals will be followed as they propagate from the KaiABC oscillator, through the
antagonistic output pathways, mediated by SasA and CikA proteins, to generate circadian
rhythms of RpaA-DNA binding. In aim 2, the temporally regulated signal transmission network
involving specific residues across KaiC (the heart of the clock) will be mapped, from sites of
phosphorylation to the KaiA-binding sites (daytime) and KaiB- and SasA-binding sites (nighttime),
using real-time NMR. Preliminary data on both aims demonstrate feasibility. This proposal is
innovative, because for the first time, it will be possible to observe the rippling of time signals
across the lengths of circadian clock proteins and their transmission from one clock component to
the next, cycle after circadian cycle, in real time. This proposal is significant, because resolving
temporal interactions within and between clock components will reveal the dynamic machinery
that generates and propagates waves of clock signals, and thereby provide insights into
biological timekeeping that are unobtainable from static structures.

## Key facts

- **NIH application ID:** 9932453
- **Project number:** 5R01GM107521-07
- **Recipient organization:** UNIVERSITY OF CALIFORNIA, MERCED
- **Principal Investigator:** Andy LiWang
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2020
- **Award amount:** $327,688
- **Award type:** 5
- **Project period:** 2014-05-15 → 2022-04-30

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/9932453

## Citation

> US National Institutes of Health, RePORTER application 9932453, The Linchpin that Joins the Circadian Oscillator to Clock Output (5R01GM107521-07). Retrieved via AI Analytics 2026-05-22 from https://api.ai-analytics.org/grant/nih/9932453. Licensed CC0.

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