A dichotomous choice for metazoan cells is between proliferation and differentiation. Measuring tRNA pools in various cell types, we found two distinct subsets, one that is induced in proliferating cells, and repressed otherwise, and another with the opposite signature. Correspondingly, we found that genes serving cell-autonomous functions and genes involved in multicellularity obey distinct codon usage. Proliferation-induced and differentiation-induced tRNAs often carry anticodons that correspond to the codons enriched among the cell-autonomous and the multicellularity genes, respectively. Because mRNAs of cell-autonomous genes are induced in proliferation and cancer in particular, the concomitant induction of their codon-enriched tRNAs suggests coordination between transcription and translation. Histone modifications indeed change similarly in the vicinity of cell-autonomous genes and their corresponding tRNAs, and in multicellularity genes and their tRNAs, suggesting the existence of transcriptional programs coordinating tRNA supply and demand. Hence, we describe the existence of two distinct translation programs that operate during proliferation and differentiation.

The environmentally sensitive, sulfhydryl-reactive, fluorescent probe N,N -dimethyl-N-(iodoacetyl)-N -(7-nitrobenz-2-oxa-1,3-diazol-4-yl) ethylene-diamine (IANBD) was used as a molecular reporter of agonist-induced conformational changes in the ␤ 2 adrenergic receptor, a prototype hormone-activated G protein-coupled receptor. In the background of a mutant ␤ 2 adrenergic receptor, with a minimal number of endogenous cysteine residues, new cysteines were introduced in positions 269 6.31 , 270 6.32 , 271 6.33 , and 272 6.34 at the cytoplasmic side of transmembrane segment (TM) 6. The resulting mutant receptors were fully functional and bound both agonists and antagonist with high affinities also upon IANBD labeling. Fluorescence spectroscopy analysis of the purified and site-selectively IANBD-labeled mutants suggested that the covalently attached fluorophore was exposed to a less polar environment at all four positions upon agonist binding. Whereas evidence for only a minor change in the molecular environment was obtained for positions 269 6.31 and 270 6.32 , the full agonist isoproterenol caused clear dose-dependent and reversible increases in fluorescence emission at positions 271 6.33 and 272 6.34 . The data suggest that activation of G proteincoupled receptors, which are activated by "diffusible" ligands, involves a structural rearrangement corresponding to the cytoplasmic part of TM 6. The preferred conformations of the IANBD moiety attached to the inserted cysteines were predicted by employing a computational method that incorporated the complex hydrophobic/hydrophilic environment in which the cysteines reside. Based on these preferred conformations, it is suggested that the spectral changes reflect an agonistpromoted movement of the cytoplasmic part of TM 6 away from the receptor core and upwards toward the membrane bilayer.G protein-coupled receptors (GPCRs), 1 or seven-transmembrane segment receptors, comprise the largest superfamily of mammalian proteins with now more than 1000 different members (1, 2). The ␤ 2 -adrenergic receptor (␤2AR) was cloned more than a decade ago and has since served as a prototypic member of the receptor family (3, 4). A key issue in our understanding of GPCR function is the nature of the molecular mechanisms that couple agonist binding to receptor activation and transmission of the signal across the plasma membrane. Only recently spectroscopic techniques on purified receptor preparations have been taken into use and permitted the first direct insight into structural changes that occur during receptor activation (4). The use of EPR spectroscopy by Hubbell, Khorana, and co-workers (5-7) has showed evidence that activation of the light-sensing receptor rhodopsin involves movements of transmembrane segment (TM) 3 and 6 relative to one another. In addition, movements of TM 6 in rhodopsin have been predicted from fluorescence spectroscopy studies (8). Our application of fluorescence spectroscopy to the ␤2AR has supported a role of TM 3 and 6 also for activation of GPCRs activated by ...

The discovery that the Ten-Eleven Translocation (TET) hydroxylases cause DNA demethylation has fundamentally changed the notion of how DNA methylation is regulated. Clonal analysis of the hematopoetic stem cell compartment suggests that TET2 mutations can be early events in hematologic cancers and recent investigations have shown TET2 mutations in diffuse large B-cell lymphoma. However, the detection rates and the types of TET2 mutations vary, and the relation to global methylation patterns has not been investigated. Here, we show TET2 mutations in 12 of 100 diffuse large B-cell lymphomas with 7% carrying loss-of-function and 5% carrying missense mutations. Genome-wide methylation profiling using 450K Illumina arrays identified 315 differentially methylated genes between TET2 mutated and TET2 wild-type cases. TET2 mutations are primarily associated with hypermethylation within CpG islands (70%; P<0.0001), and at CpG-rich promoters (60%; P<0.0001) of genes involved in hematopoietic differentiation and cellular development. Hypermethylated loci in TET2 muta ted samples overlap with the bivalent (H3K27me3/H3K4me3) silencing mark in human embryonic stem cells (P=1.5x10 -30 ). Surprisingly, gene expression profiling showed that only 11% of the hypermethylated genes were down-regulated, among which there were several genes previously suggested to be tumor suppressors. A metaanalysis suggested that the 35 hypermethylated and down-regulated genes are associated with the activated B-celllike type of diffuse large B-cell lymphoma in other studies. In conclusion, our data suggest that TET2 mutations may cause aberrant methylation mainly of genes involved in hematopoietic development, which are silenced but poised for activation in human embryonic stem cells.Genome-wide profiling identifies a DNA methylation signature that associates with TET2 mutations in diffuse large B-cell lymphoma