Analysis of expressed sequence tags from oil palm (Elaeis guineensis)

This is the first report of a systematic study of genes expressed by means of expressed sequence tag (EST) analysis in oil palm, a species of the Arecales order, a phylogenetically key clade of monocotyledons that is not widely represented in the sequence databases. Five different cDNA libraries were generated from male and female inflorescences, shoot apices and zygotic embryos and unidirectional systematic sequencing was performed. A total of 2411 valid EST sequences were thus obtained. Cluster analysis enabled the identification of 209 groups of related sequences and 1874 singletons. Putative functions were assigned to 1252 of the set of 2083 non-redundant ESTs obtained. The EST database described here is a first step towards gene discovery and cDNA array-based expression analysis in oil palm.     

Changes in nucleoporin domain topology in response to chemical effectors

Nucleoporins represent the molecular building blocks of nuclear pore complexes (NPCs), which mediate facilitated macromolecular trafficking between the cytoplasm and nucleus of eukaryotic cells. Phenylalanine-glycine (FG) repeat motifs are found in about one-third of the nucleoporins, and they provide major binding or docking sites for soluble transport receptors. We have shown recently that localization of the FG-repeat domains of vertebrate nucleoporins Nup153 and Nup214 within the NPC is influenced by its transport state. To test whether chemical effectors, such as calcium and ATP, influence the localization of the FG-repeat domains of Nup153 and Nup214 within the NPC, we performed immuno-electron microscopy of Xenopus oocyte nuclei using domain-specific antibodies against Nup153 and Nup214, respectively. Ca2+ and ATP are known to induce conformational changes in the NPC architecture, especially at the cytoplasmic face, but also at the nuclear basket of the NPC. We have found concentrations of calcium in the micromolar range or 1 mM ATP in the surrounding buffer leaves the spatial distribution of the FG-repeat of Nup153 and Nup214 largely unchanged. In contrast, ATP depletion, calcium store depletion by EGTA or thapsigargin, and high concentrations of divalent cation (i.e. 2 mM Ca2+ and 2 mM Mg2+) constrain the distribution of the FG-repeats of Nup153 and Nup214. Our data suggest that the location of the FG-repeat domains of Nup153 and Nup214 is sensitive to chemical changes within the near-field environment of the NPC.     

Nuclear localization signal-dependent and -independent movements of Drosophila melanogaster dUTPase isoforms during nuclear cleavage

Two dUTPase isoforms (23 kDa and 21 kDa) are present in the fruitfly with the sole difference of an N-terminal extension. In Drosophila embryo, both isoforms are detected inside the nucleus. Here, we investigated the function of the N-terminal segment using eYFP-dUTPase constructs. In Schneider 2 cells, only the 23 kDa construct showed nuclear localization arguing that it may contain a nuclear localization signal (NLS). Sequence comparisons identified a lysine-rich nonapeptide with similarity to the human c-myc NLS. In Drosophila embryos during nuclear cleavages, the 23 kDa isoform showed the expected localization shifts. Contrariwise, although the 21 kDa isoform was excluded from the nuclei during interphase, it was shifted to the nucleus during prophase and forthcoming mitotic steps. The observed dynamic localization character showed strict timing to the nuclear cleavage phases and explained how both isoforms can be present within the nuclear microenvironment, although at different stages of cell cycle.     

Expanding the annotation of zebrafish microRNAs based on small RNA sequencing

MicroRNAs (miRs) are short non-coding RNAs that fine-tune the regulation of gene expression to coordinate a wide range of biological processes. Because of their role in the regulation of gene expression, miRs are essential players in development by acting on cell fate determination and progression towards cell differentiation and are increasingly relevant to human health and disease. Although the zebrafish Danio rerio is a major model for studies of development, genetics, physiology, evolution, and human biology, the annotation of zebrafish miR-producing genes remains limited. In the present work, we report deep sequencing data of zebrafish small RNAs from brain, heart, testis, and ovary. Results provide evidence for the expression of 56 un-annotated mir genes and 248 un-annotated mature strands, increasing the number of zebrafish mir genes over those already deposited in miRBase by 16% and the number of mature sequences by 63%. We also describe the existence of three pairs of mirror-mir genes and two mirtron genes, genetic features previously undescribed in non-mammalian vertebrates. This report provides information that substantially increases our knowledge of the zebrafish miRNome and will benefit the entire miR community.     

A complex peptide-sorting signal, but no mRNA signal, is required for the Sec-independent transport of Ist2 from the yeast ER to the plasma membrane

The yeast integral plasma membrane protein Ist2 belongs to a group of membrane proteins which are synthesized from localized mRNAs. The protein reaches the plasma membrane via the ER on a route operating independently of the classical secretory pathway. We have identified a complex peptide-sorting signal located at the extreme C-terminus. This sorting signal operates independently of targeting information in IST2 mRNA and sorting to the plasma membrane does not require She-mediated mRNA transport into daughter cells. Based on these results, we suggest a posttranslational mechanism, which leads to the concentration of Ist2--via multimerization--at ER sites, followed by direct transport to the plasma membrane. This novel mechanism operates downstream of IST2 mRNA localization.     

Hepatitis C virus NS5A protein modulates template selection by the RNA polymerase in in vitro system

Hepatitis C virus (HCV) NS5A phosphoprotein is a component of virus replicase. Here we demonstrate that in vitro unphosphorylated NS5A protein inhibits HCV RNA-dependent RNA polymerase (RdRp) activity in polyA-oligoU system but has little effect on synthesis of viral RNA. The phosphorylated casein kinase (CK) II NS5A protein causes the opposite effect on RdRp in each of these systems. The phosphorylation of NS5A protein with CKII does not affect its affinity to the HCV RdRp and RNA. The NS5A phosphorylation with CKI does not change the RdRp activity. Herein we report evidence that the NS5A prevents template binding to the RdRp.

Structured summary

MINT-6803697: CKI (uniprotkb:P97633) phosphorylates (MI:0217) NS5A (uniprotkb:P26662) by protein kinase assay (MI:0424)MINT-6803713: CKII (uniprotkb:P67870) phosphorylates (MI:0217) NS5A (uniprotkb:P26662) by protein kinase assay (MI:0424)     

A homemade MLPA assay detects known CTNS mutations and identifies a novel deletion in a previously unresolved cystinosis family

Infantile nephropatic cystinosis is a rare, recessive, and genetically homogeneous disorder impairing renal function. It is caused by mutations in CTNS. Several large copy number aberrations have been identified but, for the majority of these, heterozygous patients and carriers can not easily be identified. We therefore developed a multiplex ligation-dependent probe amplification assay targeting eight of the twelve CTNS exons. We show that this assay is valid in detecting known deletions in both the homozygous and heterozygous state. The application to a family previously found mutation-negative by conventional screening revealed a novel large deletion which, as the first of its kind, does not involve the coding region. We conclude that our assay represents a valid tool for further completing the CTNS mutation spectrum and for simplified carrier testing in cystinosis families harboring copy number mutations. More generally, our study exemplifies the use of synthetic, homemade MLPA probesets as cheap, efficient, and rapidly available screening tools for small genes and/or very rare diseases.     

Domain topology of the p62 complex within the 3-D architecture of the nuclear pore complex

The nuclear pore complex (NPC) is the only known gateway for exchange of macromolecules between the cytoplasm and nucleus of eukaryotic cells. One key compound of the NPC is the p62 subcomplex, which consists of the nucleoporins p62, p54, and p58/p45 and is supposed to be involved in nuclear protein import and export. Here we show the localization of distinct domains of the p62 complex by immuno-electron microscopy using isolated nuclei from Xenopus oocytes. To determine the exact position of the p62 complex, we examined the localization of the C and N-terminal domains of p62 by immunogold-labeling using domain-specific antibodies against p62. In addition we expressed epitope-tagged versions of p62, p54, and p58 in Xenopus oocytes and localized the domains with antibodies against the tags. This first systematic analysis of the domain topology of the p62 complex within the NPC revealed that the p62 complex is anchored to the cytoplasmic face of the NPC most likely by the coiled-coil domains of the three nucleoporins. Furthermore, we found the phenylalanine-glycine (FG)-repeat domain of p62, but not of p58 and p54, to be of mobile and flexible nature.     

Crystallographic and Biochemical Analysis of the Ran-binding Zinc Finger Domain

The nuclear pore complex (NPC) resides in circular openings within the nuclear envelope and serves as the sole conduit to facilitate nucleocytoplasmic transport in eukaryotes. The asymmetric distribution of the small G protein Ran across the nuclear envelope regulates directionality of protein transport. Ran interacts with the NPC of metazoa via two asymmetrically localized components, Nup153 at the nuclear face and Nup358 at the cytoplasmic face. Both nucleoporins contain a stretch of distinct, Ran-binding zinc finger domains. Here, we present six crystal structures of Nup153-zinc fingers in complex with Ran and a 1.48 Å crystal structure of RanGDP. Crystal engineering allowed us to obtain well diffracting crystals so that all ZnF-Ran complex structures are refined to high resolution. Each of the four zinc finger modules of Nup153 binds one Ran molecule in apparently non-allosteric fashion. The affinity is measurably higher for RanGDP than for RanGTP and varies modestly between the individual zinc fingers. By microcalorimetric and mutational analysis, we determined that one specific hydrogen bond accounts for most of the differences in the binding affinity of individual zinc fingers. Genomic analysis reveals that only in animals do NPCs contain Ran-binding zinc fingers. We speculate that these organisms evolved a mechanism to maintain a high local concentration of Ran at the vicinity of the NPC, using this zinc finger domain as a sink.     

The crystal structure of the C-terminal DAP5/p97 domain sheds light on the molecular basis for its processing by caspase cleavage

DAP5/p97 (death-associated protein 5) is a member of the eukaryotic translation initiation factor 4G family. It functions as a scaffold protein promoting cap-independent translation of proteins. During apoptosis, DAP5/p97 is cleaved by caspases at position 792, yielding an 86-kDa C-terminal truncated isoform (DAP5/p86) that promotes translation of several mRNAs mediated by an internal ribosome entry site. In this study, we report the crystal structure of the C-terminal region of DAP5/p97 extending between amino acids 730 and 897. This structure consists of four HEAT-Repeats and is homologous to the C-terminal domain of eIF4GI, eIF5, and eIF2Bε. Unlike the other proteins, DAP5/p97 lacks electron density in the loop connecting α3 and α4, which harbors the caspase cleavage site. Moreover, we observe fewer interactions between these two helices. Thus, previous mapping of this site by mutation analysis is confirmed here by the resolved structure of the DAP5/p97 C-terminus. In addition, we identified the position of two conserved aromatic and acidic boxes in the structure of the DAP5/p97 C-terminus. The acidic residues in the two aromatic and acidic boxes form a continuous negatively charged patch, which is suggested to make specific interactions with other proteins such as eIF2β. The caspase cleavage of DAP5/p97 removes the subdomain carrying acidic residues in the AA-box motif, which may result in exposure of a hydrophobic surface. These intriguing structural differences between the two DAP5 isoforms suggest that they have different interaction partners and, subsequently, different functions.     

The inner nuclear membrane protein Lem2 is critical for normal nuclear envelope morphology

The inner nuclear membrane (INM) of eukaryotic cells is characterized by a unique set of transmembrane proteins which interact with chromatin and/or the nuclear lamina. The number of identified INM proteins is steadily increasing, mainly as a result of proteomic and computational approaches. However, despite a link between mutation of several of these proteins and disease, the function of most transmembrane proteins of the INM remains unknown and depletion of many of these proteins from a variety of systems did not produce an obvious phenotype in the affected cells. Here, we report that depletion of the conserved INM protein Lem2 from human cell lines leads to abnormally shaped nuclei and severely reduces cell survival. We suggest that interactions of Lem2 with lamins or chromatin are critical for maintaining the integrity of the nuclear envelope.     

Constitutive Nuclear Localization of an Alternatively Spliced Sirtuin-2 Isoform

Sirtuin-2 (SIRT2), the cytoplasmic member of the sirtuin family, has been implicated in the deacetylation of nuclear proteins. Although the enzyme has been reported to be located to the nucleus during G₂/M phase, its spectrum of targets suggests functions in the nucleus throughout the cell cycle. While a nucleocytoplasmic shuttling mechanism has been proposed for SIRT2, recent studies have indicated the presence of a constitutively nuclear isoform. Here we report the identification of a novel splice variant (isoform 5) of SIRT2 that lacks a nuclear export signal and encodes a predominantly nuclear isoform. This novel isoform 5 fails to show deacetylase activity using several assays, both in vitro and in vivo, and we are led to conclude that this isoform is catalytically inactive. Nevertheless, it retains the ability to interact with p300, a known interaction partner. Moreover, changes in intrinsic tryptophan fluorescence upon denaturation indicate that the protein is properly folded. These data, together with computational analyses, confirm the structural integrity of the catalytic domain. Our results suggest an activity-independent nuclear function of the novel isoform.     

Nucleosome deposition and DNA methylation may participate in the recognition of premature termination codon in nonsense-mediated mRNA decay

In non-mammalian eukaryotes, an abnormally long 3′ untranslated region (UTR) is generally thought to be the definitive signal in the recognition of a premature termination codon (PTC) in nonsense-mediated mRNA decay (NMD). However, because the lengths of 3′ UTRs in normal mRNAs are widely distributed, “abnormally long” is hard to define. Distinct peaks of nucleosome deposition and DNA methylation have recently been found at coding region boundaries. We propose that nucleosomes and DNA methylation just upstream of a normal stop codon are ideal indicators for the position of a normal stop codon and may thus serve as signals in PTC recognition.     

Exclusion of mRNPs and ribosomal particles from a thin zone beneath the nuclear envelope revealed upon inhibition of transport

We have studied the nucleocytoplasmic transport of a specific messenger RNP (mRNP) particle, named Balbiani ring (BR) granule, and ribosomal RNP (rRNP) particles in the salivary glands of the dipteran Chironomus tentans. The passage of the RNPs through the nuclear pore complex (NPC) was inhibited with the nucleoporin-binding wheat germ agglutinin, and the effects were examined by electron microscopy. BR mRNPs bound to the nuclear basket increased in number, while BR mRNPs translocating through the central channel decreased, suggesting that the initiation of translocation proper had been inhibited. The rRNPs accumulated heavily in nucleoplasm, while no or very few rRNPs were recorded within nuclear baskets. Thus, the transport of rRNPs had been blocked prior to the entry into the baskets. Remarkably, the rRNPs had been excluded both from baskets and the space in between the baskets. We propose that normally basket fibrils move freely and repel RNPs from the exclusion zone unless the particles have affinity for and bind to nucleoporins within the baskets.     

Two distinct human POM121 genes: requirement for the formation of nuclear pore complexes

Pom121 is one of the integral membrane components of the nuclear pore complex (NPC) in vertebrate cells. Unlike rodent cells carrying a single POM121 gene, human cells possess multiple POM121 gene loci on chromosome 7q11.23, as a consequence of complex segmental-duplications in this region during human evolution. In HeLa cells, two "full-length" Pom121 are transcribed and translated by two distinct genetic loci. RNAi experiments showed that efficient depletion of both Pom121 proteins significantly reduces assembled NPCs on nuclear envelope. Pom121-depletion also induced clustering of NPCs, indicating its role on maintenance of NPC structure/organization.