The experiments kinetically characterize all major steps of the initiation process, revealing heretofore unknown features, including reversible formation of two closed complexes with greatly differing stabilities, multiple attempts for each successful formation of an open complex, and efficient release of σ 54 from the polymerase core at the start of transcript synthesis. We used a multiwavelength single-molecule fluorescence colocalization approach, CoSMoS, to define the initiation pathway at an activator-dependent bacterial σ 54 promoter that recapitulates characteristic features of eukaryotic promoters activated by enhancer binding proteins.
By comparing domain formation by Turing and bistable-switch mechanisms in these contexts, we show that bistable switching provides a superior account of nucleation and confinement of the stem cell domain under reasonable assumptions on reaction rates and diffusion constants.Understanding the pathway and kinetic mechanisms of transcription initiation is essential for quantitative understanding of gene regulation, but initiation is a multistep process, the features of which can be obscured in bulk analysis.
We study the bistable-switch mechanism for pattern formation in a spatially continuous domain and in a discrete cellularized tissue in the presence of a non-uniform field of a rapidly diffusing hormone. As an alternative mechanism, we propose a model for stem cell confinement based on a bistable-switch in WUSCHEL–CLAVATA interactions. However, Turing patterns have certain properties that are inconsistent with observed patterns of stem cell differentiation in the SAM. This classic activator–inhibitor network can generate localized patterns of WUSCHEL activity by a Turing instability provided certain constraints on reaction rates and diffusion constants of WUSCHEL and CLAVATA are satisfied, and most existing mathematical models of nucleation and confinement of stem cells in the SAM rely on Turing's mechanism. WUSCHEL expression is self-activating and downregulated by a signaling pathway initiated by CLAVATA proteins, which are upregulated by WUSCHEL. This reservoir of stem cells is maintained by expression of a transcription factor WUSCHEL that is responsible for the development of stem cells in the central zone.
Expansion of meristematic tissue is derived from the growth and division of stem cells that reside in a central zone of the SAM. Shoot apical meristems (SAMs) give rise to all above-ground tissues of a plant.
0 kommentar(er)
