Spatial effects on the speed and reliability of protein-DNA search

TL;DR

This paper investigates how spatial effects influence the speed and reliability of protein-DNA search mechanisms, highlighting local diffusion, search types, and their biological implications.

Contribution

It distinguishes between local and global search modes, analyzes their impact on search efficiency, and discusses biological strategies for rapid gene regulation.

Findings

Local 3D diffusion often occurs near dissociation sites.

Global and local searches differ significantly in search time and variability.

Search times are longer than optimal due to unbalanced 1D and 3D search contributions.

Abstract

Strong experimental and theoretical evidence shows that transcription factors and other specific DNA-binding proteins find their sites using a two-mode search: alternating between 3D diffusion through the cell and 1D sliding along the DNA. We consider the role spatial effects in the mechanism on two different scales. First, we reconcile recent experimental findings by showing that the 3D diffusion of the transcription factor is often local, i.e. the transcription factor lands quite near its dissociation site. Second, we discriminate between two types of searches: global searches and local searches. We show that these searches differ significantly in average search time and the variability of search time. Using experimentally measured parameter values, we also show that 1D and 3D search is not optimally balanced, leading to much larger estimates of search time. Together, these results lead to a number of biological implications including suggestions of how prokaryotes and eukaryotes achieve rapid gene regulation and the relationship between the search mechanism and noise in gene expression.