Improved computational analysis of ribosome dynamics from 5'P degradome data using fivepseq

Comparison of Xrn1 and Rat1 5' → 3' exoribonucleases in budding yeast supports the specific role of Xrn1 in cotranslational mRNA decay

The yeast Saccharomyces cerevisiae and most eukaryotes carry two 5' → 3' exoribonuclease paralogs. In yeast, they are called Xrn1, which shuttles between the nucleus and the cytoplasm, and executes major cytoplasmic messenger RNA (mRNA) decay, and Rat1, which carries a strong nuclear localization sequence (NLS) and localizes to the nucleus. Xrn1 is 30% identical to Rat1 but has an extra ~500 amino acids C-terminal extension. In the cytoplasm, Xrn1 can degrade decapped mRNAs during the last round of translation by ribosomes, a process referred to as "cotranslational mRNA decay." The division of labor between the two enzymes is still enigmatic and serves as a paradigm for the subfunctionalization of many other paralogs. Here we show that Rat1 is capable of functioning in cytoplasmic mRNA decay, provided that Rat1 remains cytoplasmic due to its NLS disruption (cRat1). This indicates that the physical segregation of the two paralogs plays roles in their specific functions. However, reversing segregation is not sufficient to fully complement the Xrn1 function. Specifically, cRat1 can partially restore the cell volume, mRNA stability, the proliferation rate, and 5' → 3' decay alterations that characterize xrn1Δ cells. Nevertheless, cotranslational decay is only slightly complemented by cRat1. The use of the AlphaFold prediction for cRat1 and its subsequent docking with the ribosome complex and the sequence conservation between cRat1 and Xrn1 suggest that the tight interaction with the ribosome observed for Xrn1 is not maintained in cRat1. Adding the Xrn1 C-terminal domain to Rat1 does not improve phenotypes, which indicates that lack of the C-terminal is not responsible for partial complementation. Overall, during evolution, it appears that the two paralogs have acquired specific characteristics to make functional partitioning beneficial.

Cellular energy regulates mRNA degradation in a codon-specific manner

Codon optimality is a major determinant of mRNA translation and degradation rates. However, whether and through which mechanisms its effects are regulated remains poorly understood. Here we show that codon optimality associates with up to 2-fold change in mRNA stability variations between human tissues, and that its effect is attenuated in tissues with high energy metabolism and amplifies with age. Mathematical modeling and perturbation data through oxygen deprivation and ATP synthesis inhibition reveal that cellular energy variations non-uniformly alter the effect of codon usage. This new mode of codon effect regulation, independent of tRNA regulation, provides a fundamental mechanistic link between cellular energy metabolism and eukaryotic gene expression.

Atlas of mRNA translation and decay for bacteria

Regulation of messenger RNA stability is pivotal for programmed gene expression in bacteria and is achieved by a myriad of molecular mechanisms. By bulk sequencing of 5' monophosphorylated mRNA decay intermediates (5'P), we show that cotranslational mRNA degradation is conserved among both Gram-positive and -negative bacteria. We demonstrate that, in species with 5'-3' exonucleases, the exoribonuclease RNase J tracks the trailing ribosome to produce an in vivo single-nucleotide toeprint of the 5' position of the ribosome. In other species lacking 5'-3' exonucleases, ribosome positioning alters endonucleolytic cleavage sites. Using our metadegradome (5'P degradome) sequencing approach, we characterize 5'P mRNA decay intermediates in 96 species including Bacillus subtilis, Escherichia coli, Synechocystis spp. and Prevotella copri and identify codon- and gene-level ribosome stalling responses to stress and drug treatment. We also apply 5'P sequencing to complex clinical and environmental microbiomes and demonstrate that metadegradome sequencing provides fast, species-specific posttranscriptional characterization of responses to drug or environmental perturbations. Finally we produce a degradome atlas for 96 species to enable analysis of mechanisms of RNA degradation in bacteria. Our work paves the way for the application of metadegradome sequencing to investigation of posttranscriptional regulation in unculturable species and complex microbial communities.

Copy number variation in tRNA isodecoder genes impairs mammalian development and balanced translation

The number of tRNA isodecoders has increased dramatically in mammals, but the specific molecular and physiological reasons for this expansion remain elusive. To address this fundamental question we used CRISPR editing to knockout the seven-membered phenylalanine tRNA gene family in mice, both individually and combinatorially. Using ATAC-Seq, RNA-seq, ribo-profiling and proteomics we observed distinct molecular consequences of single tRNA deletions. We show that tRNA-Phe-1-1 is required for neuronal function and its loss is partially compensated by increased expression of other tRNAs but results in mistranslation. In contrast, the other tRNA-Phe isodecoder genes buffer the loss of each of the remaining six tRNA-Phe genes. In the tRNA-Phe gene family, the expression of at least six tRNA-Phe alleles is required for embryonic viability and tRNA-Phe-1-1 is most important for development and survival. Our results reveal that the multi-copy configuration of tRNA genes is required to buffer translation and viability in mammals.

Structural basis for PoxtA-mediated resistance to phenicol and oxazolidinone antibiotics

PoxtA and OptrA are ATP binding cassette (ABC) proteins of the F subtype (ABCF). They confer resistance to oxazolidinone and phenicol antibiotics, such as linezolid and chloramphenicol, which stall translating ribosomes when certain amino acids are present at a defined position in the nascent polypeptide chain. These proteins are often encoded on mobile genetic elements, facilitating their rapid spread amongst Gram-positive bacteria, and are thought to confer resistance by binding to the ribosome and dislodging the bound antibiotic. However, the mechanistic basis of this resistance remains unclear. Here we refine the PoxtA spectrum of action, demonstrate alleviation of linezolid-induced context-dependent translational stalling, and present cryo-electron microscopy structures of PoxtA in complex with the Enterococcus faecalis 70S ribosome. PoxtA perturbs the CCA-end of the P-site tRNA, causing it to shift by ∼4 Å out of the ribosome, corresponding to a register shift of approximately one amino acid for an attached nascent polypeptide chain. We postulate that the perturbation of the P-site tRNA by PoxtA thereby alters the conformation of the attached nascent chain to disrupt the drug binding site.

PoxtA confers resistance to ribosome-targeting oxazolidinone (linezolid) and chloramphenicol antibiotics. Here, Crowe-McAuliffe et al. provide structural insights into how binding of PoxtA to the ribosome indirectly promotes drug dissociation.

Application of high-throughput 5'P sequencing for the study of co-translational mRNA decay

mRNA degradation is connected to the translation process up to the degree that 5'-3' mRNA degradation follows the last translating ribosome. To study 5'-3'co-translational mRNA decay and the associated ribosome dynamics, here we present an improved high-throughput 5'P degradome RNA sequencing protocol (HT-5Pseq). We exemplify its application in Saccharomyces cerevisiae, but in principle, it could be applied to any other eukaryotic organism. HT-5Pseq is easy, scalable, and uses affordable duplex-specific nuclease-based rRNA depletion. For complete details on the use and execution of this protocol, please refer to Zhang and Pelechano (2021).

Fast and Efficient 5'P Degradome Library Preparation for Analysis of Co-Translational Decay in Arabidopsis

The recent development of high-throughput technologies based on RNA sequencing has allowed a better description of the role of post-transcriptional regulation in gene expression. In particular, the development of degradome approaches based on the capture of 5′monophosphate decay intermediates allows the discovery of a new decay pathway called co-translational mRNA decay. Thanks to these approaches, ribosome dynamics could now be revealed by analysis of 5′P reads accumulation. However, library preparation could be difficult to set-up for non-specialists. Here, we present a fast and efficient 5′P degradome library preparation for Arabidopsis samples. Our protocol was designed without commercial kit and gel purification and can be easily done in one working day. We demonstrated the robustness and the reproducibility of our protocol. Finally, we present the bioinformatic reads-outs necessary to assess library quality control.