PubMed Health⌕ Search

Biomedical subjects

R Aasland

Publications and source records attributed to R Aasland.

At least 19 recordsLinked to original sources
PubMed2001

The Saccharomyces cerevisiae Set1 complex includes an Ash2 homologue and methylates histone 3 lysine 4.

The SET domain proteins, SUV39 and G9a have recently been shown to be histone methyltransferases specific for lysines 9 and 27 (G9a only) of histone 3 (H3). The SET domains of the Saccharomyces cerevisiae Set1 and Drosophila trithorax proteins are closely related to each other but distinct from SUV39 and G9a. We characterized the complex associated with Set1 and Set1C and found that it is comprised of eight members, one of which, Bre2, is homologous to the trithorax-group (trxG) protein, Ash2. Set1C requires Set1 for complex integrity and mutation of Set1 and Set1C components shortens telomeres. One Set1C member, Swd2/Cpf10 is also present in cleavage polyadenylation factor (CPF). Set1C methylates lysine 4 of H3, thus adding a new specificity and a new subclass of SET domain proteins known to methyltransferases. Since methylation of H3 lysine 4 is widespread in eukaryotes, we screened the databases and found other Set1 homologues. We propose that eukaryotic Set1Cs are H3 lysine 4 methyltransferases and are related to trxG action through association with Ash2 homologues.

Amino Acid Sequence↗
PubMed2001

The S. cerevisiae SET3 complex includes two histone deacetylases, Hos2 and Hst1, and is a meiotic-specific repressor of the sporulation gene program.

Set3 is one of two proteins in the yeast Saccharomyces cerevisiae that, like Drosophila Trithorax, contains both SET and PHD domains. We found that Set3 forms a single complex, Set3C, with Snt1, YIL112w, Sif2, Cpr1, and two putative histone deacetylases, Hos2 and NAD-dependent Hst1. Set3C includes NAD-dependent and independent deacetylase activities when assayed in vitro. Homology searches suggest that Set3C is the yeast analog of the mammalian HDAC3/SMRT complex. Set3C represses genes in early/middle of the yeast sporulation program, including the key meiotic regulators ime2 and ndt80. Whereas Hos2 is only found in Set3C, Hst1 is also present in a complex with Sum1, supporting previous characterizations of Hst1 and Sum1 as repressors of middle sporulation genes during vegetative growth. However, Hst1 is not required for meiotic repression by Set3C, thus implying that Set3C (-Hst1) and not Hst1-Sum1, is the meiotic-specific repressor of early/middle sporulation genes.

Amino Acid Sequence↗
PubMed1999

FYVE-finger proteins--effectors of an inositol lipid.

The binding of cytosolic proteins to specific intracellular membranes containing phosphorylated derivatives of phosphatidylinositol (PtdIns) is a common theme in vital cellular processes, such as cytoskeletal function, receptor signalling and membrane trafficking. Recently, several potential effectors of the phosphoinositide 3-kinase product PtdIns 3-phosphate (PtdIns(3)P) have emerged through the observation that a conserved zinc-finger-like domain, the FYVE-finger, binds specifically to this lipid. Here we review current knowledge about the structural basis for the FYVE-PtdIns(3)P interaction, its role in membrane recruitment of proteins and the functions of FYVE-finger proteins in membrane trafficking and other cellular processes.

Amino Acid Sequence↗
PubMed1998

The genetics of epigenetics.

Cis-acting binding sites for transcription activators cannot explain the patterned expression of genes during development, nor a large range of phenomena that result from gene transplacement. Heritable states of transcriptional regression or activation sequences are influenced not only by the chromosomal context of the promoter but also by modifications of histones and DNA, and long-range interactions between distant chromosomal elements. The molecular dissection of these epigenetic phenomena has become an exciting topic of research, revealing highly conserved mechanisms at work in chromatin-mediated gene control.

Animals↗
PubMed1998

Syntaxin-16, a putative Golgi t-SNARE.

Members of the syntaxin family of integral membrane proteins have recently been implicated as vesicle receptors on target membranes, coresponsible for the specificity of intracellular membrane traffic. So far, only a small number of different mammalian syntaxins have been identified. Here we report the cloning of three new human syntaxin cDNAs, presumably originating from alternative splicing of the same transcript. Syntaxin-16A and syntaxin-16B are identical, except that the latter contains an insertion of 21 amino acid residues. Syntaxin-16C is a truncated version of syntaxin-16A, lacking the C-terminal coiled-coil and hydrophobic regions characteristic for syntaxins. Database searches identified putative yeast, plant and nematode homologues of syntaxin-16, indicating that this protein is conserved through evolution, and syntaxin-16 belongs to a new subgroup of syntaxins. Epitope-tagged syntaxin-16A and syntaxin-16B were found to colocalize with the Golgi marker beta-COP, while syntaxin-16C was found in the cytosol. Syntaxin-16A associates posttranslationally with microsomes, and appears to be transported to the Golgi via the endoplasmic reticulum. The three syntaxin-16 forms may have differential roles in intracellular trafficking.

Amino Acid Sequence↗
PubMed1997

A vasa-like gene in zebrafish identifies putative primordial germ cells.

The vasa gene is essential for germline formation in Drosophila. Vasa-related genes have been isolated from several organisms including nematode, frog and mammals. In order to gain insight into the early events in vertebrate germline development, zebrafish was chosen as a model. Two zebrafish vasa-related genes were isolated, pl10a and vlg. The pl10a gene was shown to be widely expressed during embryogenesis. The vlg gene and vasa belong to the same subfamily of RNA helicase encoding genes. Putative maternal vlg transcripts were detected shortly after fertilization and from the blastula stage onwards, expression was restricted to migratory cells most likely to be primordial germ cells.

Amino Acid Sequence↗
PubMed1996

Endosomal localization of the autoantigen EEA1 is mediated by a zinc-binding FYVE finger.

EEA1, a 162-kDa autoantigen associated with subacute cutaneous systemic lupus erythematosus, is a coiled-coil protein localized to early endosomes and cytosol. At its C terminus, the protein contains a cysteine-rich motif, which is shared with Vps27, Fab1, and Vac1, yeast proteins implicated in membrane traffic (Mu, F. T., Callaghan, J. M., Steele-Mortimer, O., Stenmark, H., Parton, R. G., Campbell, P. L., McCluskey, J., Yeo, J. P., Tock, E. P., and Toh, B. H. (1995) J. Biol. Chem. 270, 13503-13511). Here we show that this motif constitutes a genuine zinc binding domain, which we term the FYVE finger (based on the first letters of four proteins containing this motif). Profile-based data base searches identified the FYVE finger in 11 distinct proteins. The FYVE finger-containing C terminus of EEA1 was found to bind 2 mol equivalents of Zn2+. Mutations of conserved histidine and cysteine residues in the FYVE motif independently reduced zinc binding to 1 mol equivalent. Confocal immunofluorescence microscopy of transfected HEp2 cells revealed that the C-terminal part (residues 1277-1411) of EEA1 colocalizes extensively with a GTPase-deficient mutant of the early endosomal GTPase Rab5, while deletion of the FYVE finger or mutations that interfere with zinc binding cause a cytosolic localization. These results implicate the FYVE finger in the specific localization of EEA1 to endosomes.

Amino Acid Sequence↗
PubMed1996

Two variants of the pituitary specific transcription factor Pit-1 in Atlantic salmon.

We have cloned two 1.6 kb cDNAs encoding variants of the POU-type pituitary-specific transcription factor Pit-1 from Atlantic salmon. Sequence comparison with mammalian Pit-1 revealed that the POU domain was highly similar while flanking regions were less conserved. The N-terminal region contained three insertions relative to mammalian Pit-1, one of these corresponded to the insertion found in the alternatively spliced Pit-1a isoform. While two different salmon Pit-1 transcripts were expressed, alternative splicing in the 5'-region did not appear to contribute to further transcript diversity. Both salmon Pit-1 cDNAs encoded 39.5 kDa proteins that specifically bind a consensus Pit-1 recognition sequence in vitro. The salmon Pit-1 proteins also recognized the classical octamer motif; however, a point mutation in the POU homeodomain abolished this interaction.

Alternative Splicing↗
PubMed1995

The chromo shadow domain, a second chromo domain in heterochromatin-binding protein 1, HP1.

The chromo domain was originally identified as a protein sequence motif common to the Drosophila chromatin proteins, Polycomb (Pc) and heterochromatin protein 1 [HP1; Paro and Hogness (1991) Proc. Natl. Acad. Sci. USA, 88, 263-267; Paro (1990) Trends Genet., 6, 416-421]. Here we describe a second chromo domain-like motif in HP1. Subsequent refined searches identified further examples of this chromo domain variant which all occur in proteins that also have an N-terminally located chromo domain. Due to its relatedness to the chromo domain, and its occurrence in proteins that also have a classical chromo domain, we call the variant the 'chromo shadow domain'. Chromo domain-containing proteins can therefore be divided into two classes depending on the presence, for example in HP1, or absence, for example in Pc, of the chromo shadow domain. We have also found examples of proteins which have two classical chromo domains. The Schizosaccharomyces pombe SWI6 protein, involved in repression of the silent mating-type loci, is a member of the chromo shadow group. The similar modular architecture of SpSW16, HP1 and HP1-like proteins supports the model that the specificity of action of chromatin proteins is generated by combinations of protein modules.

Amino Acid Sequence↗
PubMed1993

Nuclear and mitochondrial forms of human uracil-DNA glycosylase are encoded by the same gene.

Recent cloning of a cDNA (UNG15) encoding human uracil-DNA glycosylase (UDG), indicated that the gene product of M(r) = 33,800 contains an N-terminal sequence of 77 amino acids not present in the presumed mature form of M(r) = 25,800. This led to the hypothesis that the N-terminal sequence might be involved in intracellular targeting. To examine this hypothesis, we analysed UDG from nuclei, mitochondria and cytosol by western blotting and high resolution gel filtration. An antibody that recognises a sequence in the mature form of the UNG protein detected all three forms, indicating that they are products of the same gene. The nuclear and mitochondrial form had an apparent M(r) = 27,500 and the cytosolic form an apparent M(r) = 38,000 by western blotting. Gel filtration gave essentially similar estimates. An antibody with specificity towards the presequence recognised the cytosolic form of M(r) = 38,000 only, indicating that the difference in size is due to the presequence. Immunofluorescence studies of HeLa cells clearly demonstrated that the major part of the UDG activity was localised in the nuclei. Transfection experiments with plasmids carrying full-length UNG15 cDNA or a truncated form of UNG15 encoding the presumed mature UNG protein demonstrated that the UNG presequence mediated sorting to the mitochondria, whereas UNG lacking the presequence was translocated to the nuclei. We conclude that the same gene encodes nuclear and mitochondrial uracil-DNA glycosylase and that the signals for mitochondrial translocation resides in the presequence, whereas signals for nuclear import are within the mature protein.

Amino Acid Sequence↗
PubMed1993

Growth requirements and oncogene expression in the human thyroid cell line SGHTL-34.

The SV40 T-antigen-transfected human thyroid cell line SGHTL-34 was used to investigate the effect of thyrotropin (TSH), insulin-like growth factor-1 (IGF-1) and epidermal growth factor (EGF) on c-fos and c-erbB/EGF receptor (EGF-R) mRNA expression and their role in human thyroid cell proliferation. EGF caused a transient 8- and 4-fold increase in c-fos mRNA level after 30 min in serum/hormone-deprived and in logarithmically growing cells, respectively. EGF was only mitogenic in the presence of serum, as measured by 3H-thymidine incorporation and cell counting. TSH had no detectable effect on c-fos mRNA expression and no mitogenic effect on the SGHTL-34 cells. IGF-1 showed no effect alone or in combination with EGF or TSH on either proliferation or c-fos mRNA expression. Our data suggest that increased c-fos mRNA levels are part of the mitogenic pathway, but are insufficient to engender a mitogenic response. SGHTL-34 cells produced high levels of transforming growth factor-alpha (TGF-alpha) and c-erbB/EGF-R mRNA, also seen in thyroid papillary carcinomas. The TGF-alpha protein was detected in conditioned medium from the SGHTL-34 cells, indicating that TGF-alpha may function as an autocrine growth factor. Our data show that the c-erbB/EGF-R mRNA level is regulated by growth factors and hormones in the SGHTL-34 cell line. The SGHTL-34 cells may therefore represent a useful model system for studying the role of TGF-alpha and EGF-R in thyroid carcinogenesis.

Antigens, Polyomavirus Transforming↗
PubMed1993

Expression of growth hormone genes in Atlantic salmon.

Atlantic salmon (Salmo salar) possess two genes encoding GH. We have investigated the expression of these two genes in the salmon pituitary. The transcriptional start site was localized 64 nucleotides upstream of the first methionyl codon using primer extension and 5' specific polymerase chain reaction (PCR) assays. Northern analysis revealed a major Atlantic salmon GH (salGH) transcript band of approximately 1400 nucleotides. As coexpression of the salGH genes is not discernible by transcript length, other techniques were used to assess gene activity; RNase protection analysis revealed GH transcript heterogeneity, while reverse transcription-PCR assays detected transcripts from both genes at approximately equivalent amounts. The encoded salGH protein, generated in vitro and by Escherichia coli, shares electrophoretic and immunoreactive identity with native pituitary salGH.

Animals↗
PubMed1991

Cell cycle regulation and in vitro hybrid arrest analysis of the major human uracil-DNA glycosylase.

Uracil-DNA glycosylase (UDG) is the first enzyme in the excision repair pathway for removal of uracil in DNA. In vitro transcription/translation of a cloned human cDNA encoding UDG resulted in easily measurable UDG activity. The apparent size of the primary translation product was 34 kD. Two lines of evidence indicated that this cDNA encodes the major nuclear UDG. First, in vitro translation of human fibroblast mRNA isolated from S-phase cells resulted in measurable UDG activity and this UDG translation was specifically inhibited 90% by an anti-sense UDG mRNA transcript. Secondly, cell cycle analysis revealed an 8-12 fold increase in transcript level late in the G1-phase preceding a 2-3 fold increase in total UDG activity in the S-phase. UDG degradation was found to be very slow (T1/2 approximately 30h), therefore, the rate of UDG synthesis could be derived from the rate of UDG accumulation, and was found to correlate temporarily and quantitatively with the transcript level. Inhibitor studies showed that RNA and protein synthesis was required for induction of UDG. However, specific inhibition of DNA replication with aphidicolin indicated that entrance of fibroblasts into the S-phase was not required for UDG accumulation.

Aphidicolin↗