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Summary: How CRISPR-Cas systems defend bacteria and archaea against invading genetic elements is well understood, but less is known about their regulation. In the cyanobacterium Synechocystis sp. PCC 6803, the expression of one of the three different CRISPR-Cas systems responds to changes in environmental conditions. The cas operon promoter of this system is controlled by the light- and redox-responsive transcription factor RpaB binding to an HLR1 motif, resulting in transcriptional activation at low light intensities. However, the strong promoter that drives transcription of the cognate repeat-spacer array is not controlled by RpaB. Instead, the leader transcript is bound by the redox-sensitive RNA helicase CrhR. Crosslinking coupled with mass spectrometry analysis and site-directed mutagenesis revealed six residues involved in the CrhR-RNA interaction, with C371 being critically important. Thus, the expression of a type III-Dv CRISPR-Cas system is linked to the redox status of the photosynthetic cell at the transcriptional and post-transcriptional levels.

Blockchain- and smart-contract technology enhance the effectiveness and automation of business processes. The rising interest in the development of decentralized autonomous organizations (DAO) shows that blockchain technology has the potential to reform business and society. A DAO is an organization wherein business rules are encoded in smart-contract programs that are executed when specified rules are met. The contractual- and business semantics are sine qua non for drafting a legally-binding smart contract in DAO collaborations. Several smart-contract languages (SCLs) exist, such as SPESC, or Symboleo to specify a legally-binding contract. However, their primary focus is on designing and developing smart contracts with the cooperation of IT- and non-IT users. Therefore, this paper fills a gap in the state of the art by specifying a smart-legal-contract markup language (SLCML) for legal- and business constructs to draft a legally-binding DAO. To achieve the paper objective, we first present a formal SCL ontology to describe the legal- and business semantics of a DAO. Secondly, we translate the SCL ontology into SLCML, for which we present the XML schema definition. We demonstrate and evaluate our SLCML language through the specification of a real life-inspired Sale-of-Goods contract. Finally, the SLCML use-case code is translated into Solidity to demonstrate its feasibility for blockchain platform implementations.

Cross-linking mass spectrometry (XLMS) allows mapping of protein-protein and protein-RNA interactions, but the analysis of protein-DNA complexes remains challenging. Here, the authors develop a UV light-based XLMS workflow to determine protein-DNA interfaces in reconstituted chromatin and isolated nuclei.