# Protein-mediated DNA Loop Formation and Breakdown in a Fluctuating Environment 

Yih-Fan Chen*, 1 J. N. Milstein*, 2, ∗ and Jens-Christian Meiners 2, 3 

$^{1}$Department of Biomedical Engineering, University of Michigan, Ann Arbor, Michigan 48109 

$^{2}$Department of Physics, University of Michigan, Ann Arbor, Michigan 48109 

$^{3}$LSA Biophysics, University of Michigan, Ann Arbor, Michigan 48109 

(Dated: November 12, 2018) 

## Abstract 

Living cells provide a fluctuating, out-of-equilibrium environment in which genes must coordinate cellular function. DNA looping, which is a common means of regulating transcription, is very much a stochastic process; the loops arise from the thermal motion of the DNA and other fluctuations of the cellular environment. We present single-molecule measurements of DNA loop formation and breakdown when an artificial fluctuating force, applied to mimic a fluctuating cellular environment, is imposed on the DNA. We show that loop formation is greatly enhanced in the presence of noise of only a fraction of k$_{B}$T , yet find that hypothetical regulatory schemes that employ mechanical tension in the DNA–as a sensitive switch to control transcription–can be surprisingly robust due to a fortuitous cancellation of noise effects. 

