title: Effects of post-transcriptional regulation on phenotypic noise in Escherichia coli.
abstract: Cell-to-cell variations in protein abundance, called noise, give rise to phenotypic variability between isogenic cells. Studies of noise have focused on stochasticity introduced at transcription, yet the effects of post-transcriptional regulatory processes on noise remain unknown. We study the effects of RyhB, a small-RNA of Escherichia coli produced on iron stress, on the phenotypic variability of two of its downregulated target proteins, using dual chromosomal fusions to fluorescent reporters and measurements in live individual cells. The total noise of each of the target proteins is remarkably constant over a wide range of RyhB production rates despite cells being in stress. In fact, coordinate downregulation of the two target proteins by RyhB reduces the correlation between their levels. Hence, an increase in phenotypic variability under stress is achieved by decoupling the expression of different target proteins in the same cell, rather than by an increase in the total noise of each. Extrinsic noise provides the dominant contribution to the total protein noise over the total range of RyhB production rates. Stochastic simulations reproduce qualitatively key features of our observations and show that a feed-forward loop formed by transcriptional extrinsic noise, an sRNA and its target genes exhibits strong noise filtration capabilities.
authors.affiliation: Department of Physics of Complex Systems, Weizmann Institute of Science, Rehovot 76100, Israel.
authors.forename: Rinat
authors.initials: R
authors.lastname: Arbel-Goren
authors.forename: Asaf
authors.initials: A
authors.lastname: Tal
authors.forename: Tamar
authors.initials: T
authors.lastname: Friedlander
authors.forename: Shiri
authors.initials: S
authors.lastname: Meshner
authors.forename: Nina
authors.initials: N
authors.lastname: Costantino
authors.forename: Donald L
authors.initials: DL
authors.lastname: Court
authors.forename: Joel
authors.initials: J
authors.lastname: Stavans
mesh_terms: D001426:Bacterial Proteins / Q000096:biosynthesis / Q000235:genetics; D015536:Down-Regulation; D004926:Escherichia coli / Q000235:genetics* / Q000378:metabolism; D029968:Escherichia coli Proteins / Q000096:biosynthesis / Q000235:genetics*; D015964:Gene Expression Regulation, Bacterial; D007501:Iron / Q000378:metabolism; D010641:Phenotype; D058727:RNA, Small Untranslated / Q000378:metabolism; D013482:Superoxide Dismutase / Q000096:biosynthesis / Q000235:genetics; D014158:Transcription, Genetic
chemical_list: D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; D058727:RNA, Small Untranslated; D007501:Iron; C087504:SodB protein, Bacteria; D013482:Superoxide Dismutase