Biology subjects

Hochschild, A.

Publications and source records attributed to Hochschild, A..

4 recordsLinked to original sources

bioRxiv2023

Measuring prion propagation in single bacteria elucidates mechanism of loss

Prions are self-propagating protein aggregates formed by specific proteins that can adopt alternative folds. Prions were discovered as the cause of the fatal transmissible spongiform encephalopathies in mammals, but prions can also constitute non-toxic protein-based elements of inheritance in fungi and other species. Prion propagation has recently been shown to occur in bacteria for more than a hundred cell divisions, yet a fraction of cells in these lineages lost the prion through an unknown mechanism. Here, we investigate prion propagation in single bacterial cells as they divide using microfluidics and fluorescence microscopy. We show that the propagation occurs in two distinct modes with distinct stability and inheritance characteristics. We find that the prion is lost through random partitioning of aggregates to one of the two daughter cells at division. Extending our findings to prion domains from two orthologous proteins, we observe similar propagation and loss properties. Our findings also provide support for the suggestion that bacterial prions can form more than one self-propagating state. We implement a stochastic version of the molecular model of prion propagation from yeast and mammals that recapitulates all the observed single-cell properties. This model highlights challenges for prion propagation that are unique to prokaryotes and illustrates the conservation of fundamental characteristics of prion propagation across domains of life.

microbiology↗

bioRxiv2021

A bacteria-based assay to study SARS-CoV-2 protein-protein interactions

Methods for detecting and dissecting the interactions of virally encoded proteins are essential for probing basic viral biology and providing a foundation for therapeutic advances. The dearth of targeted therapeutics for the treatment of COVID-19, an ongoing global health crisis, underscores the importance of gaining a deeper understanding of the interactions of SARS-CoV-2-encoded proteins. Here we describe the use of a convenient bacteria-based two-hybrid (B2H) system to analyze the SARS-CoV-2 proteome. We identify sixteen distinct intraviral protein-protein interactions (PPIs), involving sixteen proteins. We find that many of the identified proteins interact with more than one partner. We further show how our system facilitates the genetic dissection of these interactions, enabling the identification of selectively disruptive mutations. We also describe a modified B2H system that permits the detection of disulfide bond-dependent PPIs in the normally reducing Escherichia coli cytoplasm and we use this system to detect the interaction of the SARS-CoV-2 spike protein receptor-binding domain (RBD) with its cognate cell surface receptor ACE2. We then examine how the RBD-ACE2 interaction is perturbed by several RBD amino acid substitutions found in currently circulating SARS-CoV-2 variants. Our findings illustrate the utility of a genetically tractable bacterial system for probing the interactions of viral proteins and investigating the effects of emerging mutations. In principle, the system could also facilitate the identification of potential therapeutics that disrupt specific interactions of virally encoded proteins. More generally, our findings establish the feasibility of using a B2H system to detect and dissect disulfide bond-dependent interactions of eukaryotic proteins. ImportanceUnderstanding how virally encoded proteins interact with one another is essential in elucidating basic viral biology, providing a foundation for therapeutic discovery. Here we describe the use of a versatile bacteria-based system to investigate the interactions of the protein set encoded by SARS-CoV-2, the virus responsible for the current pandemic. We identify sixteen distinct intraviral protein-protein interactions, involving sixteen proteins, many of which interact with more than one partner. Our system facilitates the genetic dissection of these interactions, enabling the identification of selectively disruptive mutations. We also describe a modified version of our bacteria-based system that permits detection of the interaction between the SARS-CoV-2 spike protein (specifically its receptor binding domain) and its cognate human cell surface receptor ACE2 and we investigate the effects of spike mutations found in currently circulating SARS-CoV-2 variants. Our findings illustrate the general utility of our system for probing the interactions of virally encoded proteins.

molecular biology↗

bioRxiv2019

Alternative transcription cycle for bacterial RNA polymerase

RNA polymerases (RNAPs) transcribe genes through a cycle of recruitment to promoter DNA, initiation, elongation, and termination. After termination, RNAP is thought to initiate the next round of transcription by detaching from DNA and rebinding a new promoter. We used single-molecule fluorescence microscopy to observe individual RNAP molecules after transcript release at a terminator. Following termination, RNAP almost always remained bound to DNA and sometimes exhibited one-dimensional sliding over thousands of basepairs. Unexpectedly, the DNA-bound RNAP often restarted transcription, usually in reverse direction, thus producing an antisense transcript. Furthermore, we report evidence of this \"secondary initiation\" in live cells, using genome-wide RNA sequencing. These findings reveal an alternative transcription cycle that allows RNAP to reinitiate without dissociating from DNA, which is likely to have important implications for gene regulation.

biophysics↗

bioRxiv2019

Tombusvirus p19 captures RNase III-cleaved double-stranded RNAs formed by overlapping sense and antisense transcripts in E. coli

Antisense transcription is widespread in bacteria. By base pairing with overlapping sense RNAs, antisense RNAs (asRNA) can form long double-stranded RNAs (dsRNA), which are cleaved by RNase III, a dsRNA endoribonuclease. Ectopic expression of plant tombusvirus p19 in E. coli stabilizes ~21 bp dsRNA RNase III decay intermediates, which enabled us to characterize otherwise highly unstable asRNA by deep sequencing of p19-captured dsRNA and total RNA. dsRNA formed at most bacterial genes in the bacterial chromosome and in a plasmid. The most abundant dsRNA clusters were mostly formed by divergent transcription of sense and antisense transcripts overlapping at their 5-ends. The most abundant clusters included small RNAs, such as ryeA/ryeB, 4 toxin-antitoxin genes, and 3 tRNAs, and some longer coding genes, including rsd and cspD. The sense and antisense transcripts in abundant dsRNA clusters were more plentiful and had longer half-lives in RNase III mutant strains, suggesting that formation of dsRNAs promoted RNA decay at these loci. However, widespread changes in protein levels did not occur in RNase III mutant bacteria. Nonetheless, some proteins involved in antioxidant responses and glycolysis changed reproducibly. dsRNAs accumulated in bacterial cells lacking RNase III, increasing in stationary phase, and correlated with increased cell death in RNase III mutant bacteria in late stationary phase. The physiological importance of widespread antisense transcription in bacteria remains unclear but it may become important during environmental stress. Ectopic expression of p19 is a sensitive method for identifying antisense transcripts and RNase III cleavage sites in bacteria.

microbiology↗