Project description:We report the effect of degradation of CEBPA (a critical myeloid lineage transcription factor) on the occupancy of core rRNA transcription machinery on rDNA in mouse GMP cells. We generated a CEBPA-Degron line by tagging endogenous alleles of the Cebpa gene with the FKBPV degron domain, and degraded CEBPA-FKBPV-FLAG fusion protein using dTAGV-1 ligand. We used anti-FLAG pulldown to demonstrate binding of CEBPA protein to rDNA at a conserved motif within the 18S transcribed region. On degradation of CEBPA, we found that RPA194 (component of Pol I) and RRN3 occupancy on rDNA were reduced, while the occupancy of upstream factors TAF1B (component of SL-1) and UBTF were unchanged. In parallel, we also found that CEBPA degradation reduced nascent rRNA transcription, cellular ribosome abundance, and cell growth. Our work indicates that the cell-type-specific transcription factor CEBPA recruits the Pol I-RRN3 complex to ribosomal DNA to promote rRNA transcription.
Project description:DNA oligonucleotide microarrays were designed with 307 probes for 96 internal transcribed spacer (ITS1, located between 18S and 26S rRNA genes) sequences of known species and strains from the genus Pseudo-nitzschia (Bacillariophyceae). In addition, microarrays also carried 1893 probes targeting ITS1 aequences of marine Crenarchaeota and Alphaproteobacteria of SAR11 clade. In order to assign microarray profiles to Pseudo-nitzschia ribotypes and species and to 'train' the data analysis system, we grew cultures of Pseudo-nitzschia in the laboratory with identities confirmed through rDNA sequence analysis. In total, 9 cultures and 35 environmental water samples were hybridized to microarrays, in some cases, in duplicate or triplicate. Analysis of microarray data allowed us to identify and map Pseudo-nitzschia spp. in the coastal waters along Washington and Oregon coast of the Eastern Pacific Ocean, and to observe seasonal changes in diatom community composition.
Project description:Ribosome biogenesis is essential for protein synthesis in gene expression. Yeast eIF5B has been shown biochemically to facilitate 18S rRNA 3’ end maturation during late-40S ribosomal subunit assembly and gate the transition from translation initiation to elongation. But the effects of eIF5B have not been studied at the genome-wide level in any organism, and 18S rRNA 3’ end maturation is poorly understood in plants. Arabidopsis HOT3/eIF5B1 was found to promote development and heat-stress acclimation by translational regulation, but its molecular function remained unknown. Here, we show that HOT3 is a late-stage ribosome biogenesis factor that facilitates 18S rRNA 3’ end processing and is a translation initiation factor that globally impacts the transition from initiation to elongation. By developing and implementing 18S-ENDseq, we revealed previously unknown events in 18S rRNA 3’ end maturation or metabolism. We quantitatively defined new processing hotspots and identified adenylation as the prevalent non-templated RNA modification at the 3’ ends of pre-18S rRNAs. Aberrant 18S rRNA maturation in hot3 further activated RNAi to generate RDR1- and DCL2/4-dependent risiRNAs mainly from a 3’ portion of 18S rRNA. We further showed that risiRNAs in hot3 were predominantly localized in ribosome-free fractions not responsible for the 18S rRNA maturation or translation initiation defects in hot3. Our study uncovered the molecular function of HOT3/eIF5B1 in 18S rRNA maturation at the late-40S assembly stage and revealed the regulatory crosstalk among ribosome biogenesis, mRNA translation initiation, and siRNA biogenesis in plants.
Project description:Polyamines, such as putrescine and spermidine, are aliphatic organic compounds with multiple amino groups. They are found ubiquitously in marine systems. However, compared with the extensive studies on the concentration and fate of other dissolved organic nitrogen compounds in seawater, such as dissolved free amino acids (DFAA), investigations of bacterially-mediated polyamine transformations have been rare. Bioinformatic analysis identified genes encoding polyamine transporters in 74 of 109 marine bacterial genomes surveyed, a surprising frequency for a class of organic nitrogen compounds not generally recognized as an important source of carbon and nitrogen for marine bacterioplankton. The genome sequence of marine model bacterium Silicibacter pomeroyi DSS-3 contains a number of genes putatively involved in polyamine use, including six four-gene ATP-binding cassette transport systems. In the present study, polyamine uptake and metabolism by S. pomeroyi was examined to confirm the role of putative polyamine-related genes, and to investigate how well current gene annotations reflect function. A comparative whole-genome microarray approach (Bürgmann et al., 2007) allowed us to identify key genes for transport and metabolism of spermidine in this bacterium, and specify candidate genes for in situ monitoring of polyamine transformations in marine bacterioplankton communities.
Project description:Ribosome-associated quality control (RQC) pathways monitor and respond to stalling of translating ribosomes. Using a newly developed technique based on in vivo UV crosslinking and mass spectrometry, we identify a C-terminal region in Hel2/Rqt1 as an RNA binding domain, with amino acids L501/K502 directly interacting with RNA. In vivo crosslinking of Hel2 revealed binding to 18S rRNA and translating mRNAs. Consistent with the 18S binding site located between mRNA entrance and exit channels, Hel2 preferentially bound mRNA both upstream and downstream of the termination codon. A C-terminal truncation that deleted L501/K502, abolished crosslinking to 18S rRNA, altered mRNA binding patterns, and reduced Hel2 function comparable to hel2∆. Asc1, also participates in RQC and ASC1 deletion impaired Hel2 18S and mRNA binding. We conclude that Hel2 is recruited or stabilized on translating 40S ribosomal subunits by interactions with 18S rRNA and Asc1. Ribosome-bound Hel2 interacts with mRNA, predominately during translation termination.