# Consequences and Control of Randomness in Timing of Intracellular

> **NIH NIH R01** · UNIVERSITY OF DELAWARE · 2020 · $223,233

## Abstract

Project Summary/Abstract:
At the level of individual cells, expression of genes is inherently stochastic across organisms
ranging from prokaryotes to human cells. Stochastic expression manifests as cell-to-cell
variation in gene product levels even among isogenic cells, and this variation significantly
affects biological functions and phenotype. How cells ensure precision in the timing of key
intracellular events in the face of of stochastic expression is an intriguing fundamental problem.
One simple model for studying event timing is the phage λ's lysis system, where lysis of the
infected E. coli cell occurs when a protein, holin, reaches a critical threshold concentration in the
cell membrane. Intriguingly, preliminary data reveals precision in timing: individual cells lyse at
an optimally scheduled time with minimal statistical fluctuations in timing. The key objective of
this proposal is to use λ's lysis system to uncover regulatory mechanisms essential for
buffering noise in timing at the single-cell level. Mathematically, noise in the event timing is
investigated using the first-passage time framework, where an event is triggered when a
stochastic process (holin level) hits a threshold for the first time. Novel analytical calculations of
the first-passage time will be performed for stochastic models of gene expression and regulation
of varying complexities. Combining theoretical results with single-cell lysis time measurements
in both wild-type and mutant phages, the mechanisms controlling stochasticity in the timing of
intracellular events will be characterized. In addition, we will use combination of mathematical
models and experiments to determine how stochasticity in lysis times drives intercellular
variations in the λ progeny count per cell.
The first-passage time framework developed here is quite general as timing of diverse cellular
processes depends on regulatory molecules reaching critical threshold levels. Identification of
regulatory motifs that buffer randomness in the timing of intracellular events has consequences
for cell-cycle control and development, where precision is required for proper system
functioning. Quantitative characterization of λ's lysis system is also critical for emerging medical
applications such as using holin proteins for targeting cancer cells and pathogenic bacteria.

## Key facts

- **NIH application ID:** 9986819
- **Project number:** 5R01GM124446-04
- **Recipient organization:** UNIVERSITY OF DELAWARE
- **Principal Investigator:** Abhyudai Singh
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2020
- **Award amount:** $223,233
- **Award type:** 5
- **Project period:** 2017-08-01 → 2022-07-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/9986819

## Citation

> US National Institutes of Health, RePORTER application 9986819, Consequences and Control of Randomness in Timing of Intracellular (5R01GM124446-04). Retrieved via AI Analytics 2026-05-25 from https://api.ai-analytics.org/grant/nih/9986819. Licensed CC0.

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