Coronaviruses (family Coronaviridae, order Nidovirales) include major human and animal pathogens. They have exceptionally large RNA genomes and use complex strategies to replicate and express these genomes. Intensive research activities in recent years have significantly advanced our knowledge of the molecular mechanisms involved in coronavirus RNA synthesis. Here, we briefly review these mechanisms and focus in particular on the structures and functions of the core replication-transcription complex (RTC) and other enzyme functions that can be recruited to this complex to fulfil additional functions, for example, in the context of 5' capping of viral mRNAs or in the context of mechanisms that control the processivity, replication fidelity, and backtracking of RTCs. Some of these recent studies provided fundamentally new insight into specific roles of previously identified genetic markers of coronaviruses and other nidoviruses, including specific functions in an unconventional RNA capping mechanism and potential roles in proofreading and discontinuous negative-strand RNA synthesis.

The eleven known zinc-dependent histone deacetylases (HDACs) catalyze the deacetylation or deacylation of myriad protein and small molecule substrates throughout the cell. The biological functions of HDACs are much more diverse than the name HDAC implies, but this name is nonetheless retained for historical purposes. The chemical mechanism of catalysis is generally conserved among HDAC isozymes: Electrophilic activation of the substrate is achieved by zinc coordination and hydrogen bonding, and nucleophilic activation of a zinc-bound water molecule is enhanced by a general base. Since aberrant activity is observed for specific HDAC isozymes in certain diseases, the development of isozyme-selective inhibitors is a current priority in worldwide medicinal chemistry campaigns. In this review, the biological functions and chemical mechanisms of the HDACs are discussed to establish the molecular context of catalysis and inhibition, particularly as the chemistry of catalysis is harnessed in the development of mechanism-based inhibitors.

In all living organisms, membrane proteins play a crucial role in governing essential biological functions, such as cellular signaling and molecular transport. These functions rely on intricate interactions with a variety of biomolecules, including substrates, proteins, metabolites, and lipids. Any disruption or alteration to these interactions can result in disease. Therefore, comprehending the complex assemblies of membrane proteins, and their intrinsic interactions, is crucial for unraveling the mechanisms of cellular regulation and has implications in disease pathology. Over the past three decades, native mass spectrometry (MS) has emerged as a pivotal tool for investigating the structure and dynamics of proteins, including membrane protein complexes. In this review, we discuss recent developments in instrumentation that advance our ability to characterize membrane proteins in their native context. As we transition toward increasingly complex eukaryotic systems, we show how this information is translated into an understanding of disease. We also highlight preliminary studies in which native MS has been used to sequence and localize membrane protein complexes within endogenous tissue. This level of detail offers the promise of informing about the molecular mechanisms of disease states.

DNA replication and transcription occur in all living cells across all domains of life. Both essential processes occur simultaneously on the same template, leading to conflicts between the macromolecular machines that perform these functions. Numerous studies over the past few decades demonstrate that this is an inevitable problem in both prokaryotic and eukaryotic cells. We have learned that conflicts lead to replication fork reversal, breaks in the DNA, R-loop formation, topological stress, and mutagenesis and can ultimately impact evolution. Recent studies have also provided insight into the various mechanisms that mitigate, resolve, and allow tolerance of conflicts and how conflicts result in pathological consequences across divergent species. In this review, we summarize our current knowledge regarding the outcomes of the encounters between replication and transcription machineries and explore how these clashes are dealt with across species.

During the last ten years, developments in cryo-electron microscopy have transformed our understanding of eukaryotic ribosome assembly. As a result, the field has advanced from a list of the vast array of ribosome assembly factors toward an emerging molecular movie in which individual frames are represented by structures of stable ribosome assembly intermediates with complementary biochemical and genetic data. In this review, we discuss the mechanisms driving the assembly of yeast and human small and large ribosomal subunits. A particular emphasis is placed on the most recent findings that illustrate key concepts of ribosome assembly, such as folding of preribosomal RNA, the enforced chronology of assembly, enzyme-mediated irreversible transitions, and proofreading of preribosomal particles.

The Annual Review of Biochemistry, in publication since 1932, sets the standard for review articles in biological chemistry and molecular biology. Since its inception, these volumes have served as an indispensable resource for both the practicing biochemist and students of biochemistry.

SMC (structural maintenance of chromosomes) protein complexes are an evolutionarily conserved family of motor proteins that hold sister chromatids together and fold genomes throughout the cell cycle by DNA loop extrusion. These complexes play a key role in a variety of functions in the packaging and regulation of chromosomes, and they have been intensely studied in recent years. Despite their importance, the detailed molecular mechanism for DNA loop extrusion by SMC complexes remains unresolved. Here, we describe the roles of SMCs in chromosome biology and particularly review in vitro single-molecule studies that have recently advanced our understanding of SMC proteins. We describe the mechanistic biophysical aspects of loop extrusion that govern genome organization and its consequences.

Messenger RNA (mRNA) stability and translational efficiency are two crucial aspects of the post-transcriptional process that profoundly impact protein production in a cell. While it is widely known that ribosomes produce proteins, studies during the past decade have surprisingly revealed that ribosomes also control mRNA stability in a codon-dependent manner, a process referred to as codon optimality. Therefore, codons, the three-nucleotide words read by the ribosome, have a potent effect on mRNA stability and provide cis-regulatory information that extends beyond the amino acids they encode. While the codon optimality molecular mechanism is still unclear, the translation elongation rate appears to trigger mRNA decay. Thus, transfer RNAs emerge as potential master gene regulators affecting mRNA stability. Furthermore, while few factors related to codon optimality have been identified in yeast, the orthologous genes in vertebrates do not necessary share the same functions. Here, we discuss codon optimality findings and gene regulation layers related to codon composition in different eukaryotic species.

Transcription-coupled repair (TCR), discovered as preferential nucleotide excision repair of UV-induced cyclobutane pyrimidine dimers located in transcribed mammalian genes compared to those in nontranscribed regions of the genome, is defined as faster repair of the transcribed strand versus the nontranscribed strand in transcribed genes. The phenomenon, universal in model organisms including Escherichia coli, yeast, Arabidopsis, mice, and humans, involves a translocase that interacts with both RNA polymerase stalled at damage in the transcribed strand and nucleotide excision repair proteins to accelerate repair. Drosophila, a notable exception, exhibits TCR but lacks an obvious TCR translocase. Mutations inactivating TCR genes cause increased damage-induced mutagenesis in E. coli and severe neurological and UV sensitivity syndromes in humans. To date, only E. coli TCR has been reconstituted in vitro with purified proteins. Detailed investigations of TCR using genome-wide next-generation sequencing methods, cryo-electron microscopy, single-molecule analysis, and other approaches have revealed fascinating mechanisms.

The insulin receptor (IR) is a type II receptor tyrosine kinase that plays essential roles in metabolism, growth, and proliferation. Dysregulation of IR signaling is linked to many human diseases, such as diabetes and cancers. The resolution revolution in cryo-electron microscopy has led to the determination of several structures of IR with different numbers of bound insulin molecules in recent years, which have tremendously improved our understanding of how IR is activated by insulin. Here, we review the insulin-induced activation mechanism of IR, including (a) the detailed binding modes and functions of insulin at site 1 and site 2 and (b) the insulin-induced structural transitions that are required for IR activation. We highlight several other key aspects of the activation and regulation of IR signaling and discuss the remaining gaps in our understanding of the IR activation mechanism and potential avenues of future research.