RESUMEN
In general, mRNAs are assumed to be loaded with ribosomes instantly upon entry into the cytoplasm. To measure ribosome density (RD) on nascent mRNA, we developed nascent Ribo-Seq by combining Ribo-Seq with progressive 4-thiouridine labeling. In mouse macrophages, we determined experimentally the lag between the appearance of nascent mRNA and its association with ribosomes, which was calculated to be 20-22 min for bulk mRNA. In mouse embryonic stem cells, nRibo-Seq revealed an even stronger lag of 35-38 min in ribosome loading. After stimulation of macrophages with lipopolysaccharide, the lag between cytoplasmic and translated mRNA leads to uncoupling between input and ribosome-protected fragments, which gives rise to distorted RD measurements under conditions where mRNA amounts are far from steady-state expression. As a result, we demonstrate that transcriptional changes affect RD in a passive way.
Asunto(s)
Biosíntesis de Proteínas , Ribosomas/genética , Ribosomas/metabolismo , Análisis de Secuencia de ARN/métodos , Animales , Citoplasma/genética , Cinética , Lipopolisacáridos/farmacología , Ratones , Células Madre Embrionarias de Ratones/citología , Células Madre Embrionarias de Ratones/fisiología , Células RAW 264.7 , ARN Mensajero/genética , Proteínas Ribosómicas/biosíntesis , Proteínas Ribosómicas/genética , Ribosomas/efectos de los fármacos , Factores de TiempoRESUMEN
Many metabolic pathways in bacteria are regulated by metabolite sensing riboswitches that exert their control at the level of transcription employing a termination-antitermination mechanism. These riboswitches represent engineering targets to modulate expression of genes and operons relevant for the biotechnological production of commercially relevant compounds. We show that removal of the transcriptional riboswitches that control purine biosynthesis and riboflavin biosynthesis in Bacillus subtilis leads to auxotrophic strains. As an alternative, we report a rational approach for engineering transcriptional riboswitches independently from the availability of structural data. This approach consists in the identification and deletion of a key nucleotide sequence exclusively involved in transcription termination without affecting formation of other secondary and tertiary structures, which can be involved in other functions. To demonstrate the efficacy of our approach, we tested it with regard to deregulation of the purine and the riboflavin biosynthetic pathways in B. subtilis. Following validation of the engineered transcriptional riboswitches using specialized reporter strains, our approach was implemented into a B. subtilis wild-type strain employing CRISPR-Cas9 genome editing. The resulting purine and riboflavin production strains were characterized at the level of gene expression, metabolite synthesis and growth, and a substantial enhancement was measured at each level. Moreover, applying our approach to deregulate the purine pathway of an industrial riboflavin overproducing strain with impaired growth led to an increase in biomass by 53%, which resulted in an enhanced total production of riboflavin in the culture.
Asunto(s)
Bacillus subtilis/metabolismo , Regulación Bacteriana de la Expresión Génica , Ingeniería Genética , Purinas/biosíntesis , ARN Bacteriano , Riboflavina/biosíntesis , Riboswitch , Transcripción Genética , Bacillus subtilis/genética , ARN Bacteriano/biosíntesis , ARN Bacteriano/genéticaRESUMEN
Tumor suppressor protein p53 protects cells against malignant transformation mostly through transcriptional activation. Lysine acetylation is required to mediate activation of p53. The protein displays eight lysine residues and their evolutionary conservation argues for an essential role. The aim of this study was to investigate the significance of individual acetylation sites in mediating p53 functions. Differences in intracellular localization, protein expression levels, and transcriptional activity were investigated by overexpressing acetylation-deficient p53 variants in the colon carcinoma-derived p53 knock-out cell line HCT 116 p53(-/-). We found that not all lysine residues are equally capable of promoting p53's functions. Individual amino acid mutations or combinations thereof led to altered p53 expression levels, intracellular distribution, or transcriptional transactivation capacity, as compared to the wild-type protein. However, we observed that the choice of protein tag and expression vector could significantly alter obtained results on certain aspects of p53 function.
Asunto(s)
Neoplasias del Colon/genética , Mutación , Proteína p53 Supresora de Tumor/genética , Acetilación , Células HCT116 , Humanos , Lisina/análisis , Lisina/genética , Mutagénesis , Activación Transcripcional , Proteína p53 Supresora de Tumor/análisisRESUMEN
The G2/M checkpoint coordinates DNA replication with mitosis and thereby prevents chromosome segregation in the presence of unreplicated or damaged DNA Here, we show that the RNA-binding protein TIAR is essential for the G2/M checkpoint and that TIAR accumulates in nuclear foci in late G2 and prophase in cells suffering from replication stress. These foci, which we named G2/M transition granules (GMGs), occur at low levels in normally cycling cells and are strongly induced by replication stress. In addition to replication stress response proteins, GMGs contain factors involved in RNA metabolism as well as CDK1. Depletion of TIAR accelerates mitotic entry and leads to chromosomal instability in response to replication stress, in a manner that can be alleviated by the concomitant depletion of Cdc25B or inhibition of CDK1. Since TIAR retains CDK1 in GMGs and attenuates CDK1 activity, we propose that the assembly of GMGs may represent a so far unrecognized mechanism that contributes to the activation of the G2/M checkpoint in mammalian cells.
Asunto(s)
Proteína Quinasa CDC2/genética , Puntos de Control de la Fase G2 del Ciclo Celular/genética , Proteínas de Unión al ARN/genética , Fosfatasas cdc25/genética , Ciclo Celular/genética , Segregación Cromosómica/genética , Daño del ADN/genética , Replicación del ADN/genética , Células HeLa , Humanos , Mitosis/genética , FosforilaciónRESUMEN
Acetylation of histones and transcription-related factors is known to exert epigenetic and transcriptional control of gene expression. Here we report that histone acetyltransferases (HATs) and histone deacetylases (HDACs) also regulate gene expression at the posttranscriptional level by controlling poly(A) RNA stability. Inhibition of HDAC1 and HDAC2 induces massive and widespread degradation of normally stable poly(A) RNA in mammalian and Drosophila cells. Acetylation-induced RNA decay depends on the HATs p300 and CBP, which acetylate the exoribonuclease CAF1a, a catalytic subunit of the CCR4-CAF1-NOT deadenlyase complex and thereby contribute to accelerating poly(A) RNA degradation. Taking adipocyte differentiation as a model, we observe global stabilization of poly(A) RNA during differentiation, concomitant with loss of CBP/p300 expression. Our study uncovers reversible acetylation as a fundamental switch by which HATs and HDACs control the overall turnover of poly(A) RNA.
