A high-resolution infrared spectroscopic investigation of the halogen atom-HCN entrance channel complexes solvated in superfluid helium droplets

Rotationally resolved infrared spectra are reported for the X-HCN (X = Cl, Br, I) binary complexes solvated in helium nanodroplets. These results are directly compared with that obtained previously for the corresponding X-HF complexes [J. M. Merritt, J. K\"upper, and R. E. Miller, PCCP, 7, 67 (2005)]. For bromine and iodine atoms complexed with HCN, two linear structures are observed and assigned to the $^{2}\Sigma_{1/2}$ and $^{2}\Pi_{3/2}$ ground electronic states of the nitrogen and hydrogen bound geometries, respectively. Experiments for HCN + chlorine atoms give rise to only a single band which is attributed to the nitrogen bound isomer. That the hydrogen bound isomer is not stabilized is rationalized in terms of a lowering of the isomerization barrier by spin-orbit coupling. Theoretical calculations with and without spin-orbit coupling have also been performed and are compared with our experimental results. The possibility of stabilizing high-energy structures containing multiple radicals is discussed, motivated by preliminary spectroscopic evidence for the di-radical Br-HCCCN-Br complex. Spectra for the corresponding molecular halogen HCN-X$_{2}$ complexes are also presented.Comment: 20 pages, 15 figures, 6 tables, RevTe

P granules extend the nuclear pore complex environment in the C. elegans germ line

Like the nuclear pore complex, FG repeat–containing P-granule proteins interact to help establish a size-exclusion barrier

Overlapping and Distinct Roles of Two C. Elegans H3 Lysine 36 Histone Methyltransferases

Establishment and maintenance of cell type-specific gene expression patterns is essential for development and normal tissue function. A growing number of studies demonstrate that epigenetic information contributes to cell fate specification and maintenance, and can be transmitted though mitotic divisions as well as from parents to progeny. Yet, the mechanisms involved in establishing and maintaining epigenetic information, as well as the consequences to gene expression in cells inheriting epigenetic information are not well understood. One form of epigenetic information, post-translational modifications of histones, can regulate gene expression patterns and provide a long-term memory of expression patterns established by transient transcription factor activity during early development. In C. elegans, two antagonistic histone methyltransferases (HMTs) are essential for germline development in a maternal effect manner. MES-2 is part of a PRC2-like complex that methylates H3 lysine 27 (H3K27me3), and MES-4 is one of two H3K36me3 HMTs. This thesis focuses on H3K36me3 and the two enzymes that generate this mark, MES-4 and MET-1. While MES-4 is required for germline development in all conditions, MET-1 is only required at elevated temperatures. Our mass spectrometry analysis of histone tails from C. elegans early embryos confirmed that both MET-1 and MES-4 catalyze H3K36me3, a modification that is generated by only a single enzyme in other organisms. We performed immunostaining studies to investigate the generation of H3K36me3 in the adult germline, its transmission from parents to progeny, and its maintenance during early embryogenesis. Our data show that MET-1 and MES-4 serve unique roles in the generation and transmission of H3K36me3. In the germline, MET-1 co-transcriptionally catalyzes H3K36me3 and is solely responsible for H3K36me3 on the oocyte X chromosome. MES-4 also contributes to H3K36me3 in the germline and is solely responsible for maintenance of H3K36me3 on chromosomes in early embryos, where it operates in a transcription-independent manner. We discovered that both oocytes and sperm transmit chromosomes carrying H3K36me3 to the embryo. This observation supports the hypothesis that epigenetic information generated in the adult germline can be transmitted to progeny from either parent. To determine if inherited H3K36me3 is required for MES-4 to associate with chromosomes, we generated embryos in which only a subset of chromosomes carry H3K36me3. In these embryos, MES-4 is recruited to H3K36me3-positive chromosomes but not to H3K36me3-negative chromosomes, suggesting MES-4 is recruited to chromosomes by pre-existing H3K36me3. Additionally, as these embryos divide, MES-4 and H3K36me3 are maintained on only a subset of chromosomes until at least the 32-cell stage, likely because MES-4 is propagating H3K36me3 in regions of chromatin with pre-existing H3K36me3. This observation suggests that MES-4 maintains an epigenetic memory of inherited H3K36me3. Together, these data support the model that MET-1 is primarily responsible for generating H3K36me3 on genes expressed in the germline, and that MES-4 is primarily responsible for maintaining an epigenetic memory of inherited H3K36me3 through early embryogenesis, likely to guide gene expression patterns in nascent germ cells

Distinct Roles of Two Histone Methyltransferases in Transmitting H3K36me3-Based Epigenetic Memory Across Generations in Caenorhabditis elegans.

Epigenetic information contributes to proper gene expression and development, and can be transmitted not only through mitotic divisions but also from parents to progeny. We investigated the roles in epigenetic inheritance of MES-4 and MET-1, the two Caenorhabditis elegans enzymes that methylate H3K36 (histone H3 Lys 36). Mass spectrometry analysis confirmed immunostaining results showing that both MES-4 and MET-1 catalyze H3K36me3. In the adult germline, MES-4 is enriched in the distal mitotic zone and MET-1 is enriched in the meiotic pachytene zone. Embryos inherit H3K36me3-marked chromosomes from both the oocyte and sperm, and a maternal load of MES-4 and MET-1 Maternal MES-4 quickly associates with sperm chromosomes; that association requires that the sperm chromosomes bear H3K36me3, suggesting that MES-4 is recruited to chromosomes by preexisting H3K36me3. In embryos that inherit H3K36me3-positive oocyte chromosomes and H3K36me3-negative sperm chromosomes, MES-4 and H3K36me3 are maintained on only a subset of chromosomes until at least the 32-cell stage, likely because MES-4 propagates H3K36me3 on regions of the genome with preexisting H3K36me3. In embryos lacking MES-4, H3K36me3 levels on chromosomes drop precipitously postfertilization. In contrast to the relatively high levels of MES-4 in early-stage embryos, MET-1 levels are low at early stages and start increasing by the ∼26-cell stage, consistent with expression from the zygotic genome. Our findings support the model that MET-1 mediates transcription-coupled H3K36me3 in the parental germline and transcriptionally active embryos, and that MES-4 transmits an epigenetic memory of H3K36me3 across generations and through early embryo cell divisions by maintaining inherited patterns of H3K36me3