The distribution of DNA replication origins across eukaryotic chromosomes is important for the replication of the genome and for genetic stability. The identity of sites in the yeast genome from which replication initiates has been known for many years, yet whether additional cis-acting sequences influence the ORC binding step, the first step of the origin cycle, is unclear. Here, the investigators employed genomic, genetic, molecular and computational experiments to discover that the conserved Fkh1 transcription factor promotes binding of chromosomal DNA by ORC at a subset of DNA replication origins. Previous data established that the functional ORC binding step occurs in G1-phase. In contrast, while it is known that Fkh1 can regulate origin activity in yeast, previously published mechanistic models support a view of Fkh1 regulation as occurring at origin activation, or the S-phase step in the origin cycle. This study defines a new mechanism by which Fkh1 can regulate origin activity ...
NAR’s Breakthrough Articles present high-impact studies answering long-standing questions in the field of nucleic acids research and/or opening up new areas and mechanistic hypotheses for investigation. These articles are chosen by the Editors on the recommendation of Editorial Board Members and Referees. Articles are accompanied by a brief synopsis explaining the findings of the paper and where they fit in the broader context of nucleic acids research. They represent the very best papers published at NAR.
The RNA exosome complex (EC) mediates processing and/or degradation of select RNAs. During erythropoiesis, the erythroid transcription factor GATA1 represses EC subunit genes. Depleting EC structural subunits prior to GATA1-mediated repression is deleterious to erythroid progenitor cells. Depletion of EC catalytic subunits Dis3 or Exosc10 in hematopoietic progenitor cells reduced erythroid progenitors and their progeny. Dis3 loss compromised erythroid progenitor and erythroblast survival, rendered erythroblasts hypersensitive to apoptosis and induced γ-H2AX, indicative of DNA double-stranded breaks. Dis3 loss-of-function phenotypes were more severe than those caused by Exosc10 depletion. The authors used a genetic rescue system to compare human Dis3 with myeloma-associated Dis3 mutants S447R and R750K. Only wild type Dis3 was competent to rescue progenitors. Dis3 establishes a disease mutation-sensitive, cell type-specific survival mechanism to enable a differentiation program.
In the ribosomal peptide synthesis, all kinds of proteinogenic aminoacyl-tRNAs (AA-tRNAs) are delivered by EF-Tu to the ribosome with similar efficiencies, which is achieved by the uniform binding affinities between those AA-tRNAs and EF-Tu. In contrast, N-methyl amino acids (MeAAs) are poorly incorporated into peptides because EF-Tu weakly binds to MeAA-tRNAs compared to the proteinogenic AA-tRNAs. To overcome this issue, the T-stem region of MeAA-tRNAs was substituted with a designer sequence, resulting in the reinforcement of their EF-Tu affinities to the comparable level with those of proteinogenic AA-tRNAs. This uniform affinity-tuning methodology has enabled the incorporation of nine distinct MeAAs into linear and thioether-macrocyclic model peptides.
