  Gene expression (GE) is an inherently random or stochastic or noisy process.
The randomness in different steps of GE, e.g., transcription, translation,
degradation, etc., leading to cell-to-cell variations in mRNA and protein
levels. This variation appears in organisms ranging from microbes to metazoans.
Stochastic gene expression has important consequences for cellular function.
The random fluctuations in protein levels produce variability in cellular
behavior. It is beneficial in some contexts and harmful to others. These
situations include stress response, metabolism, development, cell cycle,
circadian rhythms, and aging. Different model studies e.g., constitutive,
two-state, etc., reveal that the fluctuations in mRNA and protein levels arise
from different steps of gene expression among which the steps in transcription
have the maximum effect. The pulsatile mRNA production through RNAP-II based
reinitiation of transcription is an important part of gene transcription.
Though, the effect of that process on mRNA and protein levels is very little
known. The addition of any biochemical step in the constitutive or two-state
process generally decreases the mean and increases the Fano factor. In this
study, we have shown that the RNAP-II based reinitiation process in gene
transcription can have different effects on both mean and Fano factor at mRNA
levels in different model systems. It decreases the mean and Fano factor both
at the mRNA levels in the constitutive network whereas in other networks it can
simultaneously increase or decrease both quantities or it can have mixed-effect
at mRNA levels. We propose that a constitutive network with reinitiation
behaves like a product independent negative feedback circuit whereas other
networks behave as either product independent positive or negative or mixed
feedback circuit.
