Strategy of tuning gene expression ratio in prokaryotic cell from perspective of noise andcorrelation

Genes are organized into operons?in?procaryote, and these genes?in?one operon generally have related functions. However, genes?in?the same operon are usually not equally expressed, and the?ratio?needs to be fine-tuned for specific functions. We examine the difference?of?gene?expression?noise?and?correlationwhen?tuning?the?expression?level at the transcriptional or translational level?in?a bicistronic operon driven by a constitutive or a two-state promoter. We get analytic results for the?noise?and?correlation?of?gene?expression?levels, which is confirmed by our stochastic simulations. Both the?noise?and the?correlation?ofgene?expressions?in?an operon with a two-state promoter are higher than?in?an operon with a constitutive promoter. Premature termination?of?mRNA induced by transcription terminator?in?the intergenic region or changing translation rates can tune the protein?ratio?at the transcriptional level or at the translational level. We find that?gene?expression?correlation?between promoter-proximal and promoter-distal genes at the protein level decreases as termination increases.?Incontrast, changing translation rates?in?the normal range almost does not alter the?correlation. This explains why the translation rate is a key factor?ofmodulating?gene?expressions?in?an operon. Our results can be useful to understand the relationship between the operon structure and the biological function?ofa?gene?network, and also may help?in?synthetic biology design.