Biology subjects

Soulet, A.-L.

Publications and source records attributed to Soulet, A.-L..

2 recordsLinked to original sources

bioRxiv2022

Assembly mechanism and cryoEM structure of RecA recombination nucleofilaments from Streptococcus pneumoniae.

RecA-mediated Homologous Recombination (HR) is a key mechanism for genome maintenance and plasticity in bacteria. It proceeds through RecA assembly into a dynamic filament on ssDNA, the presynaptic filament, which mediates DNA homology search and ordered DNA strand exchange. Here, we combined structural, single molecule and biochemical approaches to characterize the ATP-dependent assembly mechanism of the presynaptic filament of RecA from Streptococcus pneumoniae (SpRecA), in comparison to the Escherichia coli RecA (EcRecA) paradigm. EcRecA polymerization on ssDNA is assisted by the Single-Stranded DNA Binding (SSB) protein, which unwinds ssDNA secondary structures that block EcRecA nucleofilament growth. We report that neither of the two paralogous pneumococcal SSBs could assist SpRecA polymerization on ssDNA. Instead, we found that the conserved RadA helicase promotes this SpRecA nucleofilamentation in an ATP-dependent manner. This allowed us to solve the atomic structure of such a long native SpRecA nucleopolymer by cryoEM stabilized with ATP{gamma}S. It was found to be equivalent to the crystal structure of the EcRecA filament with a marked difference in how RecA mediates nucleotide orientation in the stretched ssDNA. Then, our results show that SpRecA and EcRecA HR activities are different, in correlation with their distinct ATP-dependent ssDNA binding modes.

microbiology↗

bioRxiv2020

The alternative sigma factor σX mediates competence shut-off at the cell pole in Streptococcus pneumoniae.

Bacterial competence for genetic transformation is a well-known species-specific differentiation program driving genome plasticity, antibiotic resistance and virulence in many pathogens. How competence regulation is spatiotemporally integrated in the cell is ill-defined. Here, we unraveled the localization dynamics of the key regulators that master the two intertwined transcription waves controlling competence in Streptococcus pneumoniae. The first wave relies on a stress-inducible phosphorelay system, made up of the ComD and ComE proteins, and the second is directed by an alternative sigma factor, {sigma}X, which includes in its regulon the DprA protein that turns off competence through interaction with phosphorylated ComE. Remarkably, we found that ComD, {sigma}X and DprA stably co-localize at a single cell pole over the competence period. In contrast, ComE assembles into dynamic patches in the cell periphery, colocalizing temporarily with DprA and ComD at the pole. Furthermore, we provide evidence that {sigma}X directly conveys DprA polar anchoring. Through this protein targeting function, {sigma}X is shown to be actively involved in the timely shut-off of the competence cycle, hence preserving cell fitness. Altogether, this study unveils an unprecedented role for a bacterial transcription {sigma} factor in spatially coordinating the negative feedback loop of its own genetic circuit.

microbiology↗