Showing papers by "Nigel J. Savery published in 2019"

Direct removal of RNA polymerase barriers to replication by accessory replicative helicases.

Abstract: Bacterial genome duplication and transcription require simultaneous access to the same DNA template. Conflicts between the replisome and transcription machinery can lead to interruption of DNA replication and loss of genome stability. Pausing, stalling and backtracking of transcribing RNA polymerases add to this problem and present barriers to replisomes. Accessory helicases promote fork movement through nucleoprotein barriers and exist in viruses, bacteria and eukaryotes. Here, we show that stalled Escherichia coli transcription elongation complexes block reconstituted replisomes. This physiologically relevant block can be alleviated by the accessory helicase Rep or UvrD, resulting in the formation of full-length replication products. Accessory helicase action during replication-transcription collisions therefore promotes continued replication without leaving gaps in the DNA. In contrast, DinG does not promote replisome movement through stalled transcription complexes in vitro. However, our data demonstrate that DinG operates indirectly in vivo to reduce conflicts between replication and transcription. These results suggest that Rep and UvrD helicases operate on DNA at the replication fork whereas DinG helicase acts via a different mechanism.

Guiding Biomolecular Interactions in Cells Using de Novo Protein-Protein Interfaces

Abstract: An improved ability to direct and control biomolecular interactions in living cells would have an impact on synthetic biology. A key issue is the need to introduce interacting components that act orthogonally to endogenous proteomes and interactomes. Here, we show that low-complexity, de novo designed protein-protein interaction (PPI) domains can substitute for natural PPIs and guide engineered protein-DNA interactions in Escherichia coli. Specifically, we use de novo homo- and heterodimeric coiled coils to reconstitute a cytoplasmic split adenylate cyclase, recruit RNA polymerase to a promoter and activate gene expression, and oligomerize both natural and designed DNA-binding domains to repress transcription. Moreover, the stabilities of the heterodimeric coiled coils can be modulated by rational design and, thus, adjust the levels of gene activation and repression in vivo. These experiments demonstrate the possibilities for using designed proteins and interactions to control biomolecular systems such as enzyme cascades and circuits in cells.

A low cost, open source Turbidostat design for in-vivo control experiments in Synthetic Biology

Abstract: To characterise the dynamics of new engineered systems in Synthetic biology, continuous culture platforms are required. In this paper, after a brief review of the existing machines present in literature, we describe the design and the implementation of a new flexible and low cost turbidostat for in-vivo control experiments. Then, the results of a 3 hours long experiment of control of the Optical Density is reported. Since the foundation of our design is flexibility, in this work we also discuss some possible extensions of our design, with particular attention to their application to validate in-vivo multicellular control design.