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Biomedical subjects

J Acker

Publications and source records attributed to J Acker.

At least 19 recordsLinked to original sources
PubMed2006

Determination of manganese valency in La1-xSrxMnO3 using ELNES in the (S)TEM.

In this article several experimentally identified Mn valence-sensitive ELNES quantities for the La1-xSrxMnO3 compound class are presented, namely the energy separations between Mn-L3 and O-Ka, between O-Kb and O-Ka edges, the Mn-L2,3 white line intensity ratio, and the Mn-L3 line width. Valence sensitivities of these quantities are evaluated, and possible additional influences on them are considered. At high signal-to-noise ratio the two energy separations display most sensitively changes of the Mn valency. An experiment-based estimation of the total uncertainties of the quantities indicates that at low signal-to-noise ratio, which is the case when studying interface effects at high spatial resolution, again both energy separations allow to resolve the smallest valency changes.

Journal Article↗
PubMed2001

Autonomic responses of blood vessels and sweat glands in patients with schizophrenia treated with olanzapine or clozapine.

RATIONALE: Data comparing the in vivo effects on autonomic nervous system function of standard clinical doses of olanzapine and clozapine are sparse. OBJECTIVE: The goal of this study was to compare the skin conductance response (which is peripherally mediated via muscarinic m3-receptors) and the inspiratory gasp response (which is peripherally mediated via adrenergic receptors) between healthy controls and schizophrenics treated with clozapine or olanzapine. METHODS: Twenty patients with schizophrenia (according to DSM-III-R criteria) treated with either clozapine (200-500 mg/day) or olanzapine (10-20 mg/day) as well as ten matched controls underwent simultaneous recordings of the skin conductance response (SCR) of sweat glands and of the inspiratory gasp response (IGR) of acral blood vessels. A single, deep inspiration was used as the stimulus. Group differences for the SCR amplitudes and the post-IGR redilation times were compared using the Mann-Whitney test. RESULTS: Both clozapine- and olanzapine-treated patients showed a significant SCR reduction compared to controls. Interestingly, the reduction in SCR was significantly larger in the clozapine group compared to the olanzapine group (P<0.05). Moreover, only clozapine-treated patients showed a statistical trend towards a longer IGR redilation time compared to controls. CONCLUSION: The significantly stronger SCR reduction amongst clozapine-treated compared to olanzapine-treated patients suggests that olanzapine at a standard clinical dose exhibits a significantly smaller anticholinergic effect at peripheral m3-receptors in vivo compared to clozapine. The prolongation of IGR redilation can be explained by a prolonged release of noradrenaline due to the alpha2-antagonistic effect of clozapine.

Adult↗
PubMed1999

Brefeldin A acts to stabilize an abortive ARF-GDP-Sec7 domain protein complex: involvement of specific residues of the Sec7 domain.

We demonstrate that the major in vivo targets of brefeldin A (BFA) in the secretory pathway of budding yeast are the three members of the Sec7 domain family of ARF exchange factors: Gea1p and Gea2p (functionally interchangeable) and Sec7p. Specific residues within the Sec7 domain are important for BFA inhibition of ARF exchange activity, since mutations in these residues of Gea1p (sensitive to BFA) and of ARNO (resistant to BFA) reverse the sensitivity of each to BFA in vivo and in vitro. We show that the target of BFA inhibition of ARF exchange activity is an ARF-GDP-Sec7 domain protein complex, and that BFA acts to stabilize this complex to a greater extent for a BFA-sensitive Sec7 domain than for a resistant one.

ADP-Ribosylation Factors↗
PubMed1998

EWS, but not EWS-FLI-1, is associated with both TFIID and RNA polymerase II: interactions between two members of the TET family, EWS and hTAFII68, and subunits of TFIID and RNA polymerase II complexes.

The t(11;22) chromosomal translocation specifically linked to Ewing sarcoma and primitive neuroectodermal tumor results in a chimeric molecule fusing the amino-terminus-encoding region of the EWS gene to the carboxyl-terminal DNA-binding domain encoded by the FLI-1 gene. As the function of the protein encoded by the EWS gene remains unknown, we investigated the putative role of EWS in RNA polymerase II (Pol II) transcription by comparing its activity with that of its structural homolog, hTAFII68. We demonstrate that a portion of EWS is able to associate with the basal transcription factor TFIID, which is composed of the TATA-binding protein (TBP) and TBP-associated factors (TAFIIs). In vitro binding studies revealed that both EWS and hTAFII68 interact with the same TFIID subunits, suggesting that the presence of EWS and that of hTAFII68 in the same TFIID complex may be mutually exclusive. Moreover, EWS is not exclusively associated with TFIID but, similarly to hTAFII68, is also associated with the Pol II complex. The subunits of Pol II that interact with EWS and hTAFII68 have been identified, confirming the association with the polymerase. In contrast to EWS, the tumorigenic EWS-FLI-1 fusion protein is not associated with either TFIID or Pol II in Ewing cell nuclear extracts. These observations suggest that EWS and EWS-FLI-1 may play different roles in Pol II transcription.

Animals↗
PubMed1997

Interactions between the human RNA polymerase II subunits.

As an initial approach to characterizing the molecular structure of the human RNA polymerase II (hRPB), we systematically investigated the protein-protein contacts that the subunits of this enzyme may establish with each other. To this end, we applied a glutathione S-transferase-pulldown assay to extracts from Sf9 insect cells, which were coinfected with all possible combinations of recombinant baculoviruses expressing hRPB subunits, either as untagged polypeptides or as glutathione S-transferase fusion proteins. This is the first comprehensive study of interactions between eukaryotic RNA polymerase subunits; among the 116 combinations of hRPB subunits tested, 56 showed significant to strong interactions, whereas 60 were negative. Within the intricate network of interactions, subunits hRPB3 and hRPB5 play a central role in polymerase organization. These subunits, which are able to homodimerize and to interact, may constitute the nucleation center for polymerase assembly, by providing a large interface to most of the other subunits.

Baculoviridae↗
PubMed1997

An accurate, cost-effective approach for diagnosing retrocochlear lesions utilizing the T2-weighted, fast-spin echo magnetic resonance imaging scan.

Recent data indicate that the auditory brainstem response (ABR) fails to identify a significant number of retrocochlear lesions. Although the magnetic resonance imaging (MRI) scan with paramagnetic enhancement is highly accurate at detecting these lesions, it is time consuming and expensive. We report on our prospective evaluation of a cohort of 155 patients who underwent T2-weighted, fast-spin echo MRI scans designed to screen for retrocochlear lesions. This imaging technique is rapidly performed and provides superb visualization of the relevant anatomic structures at a global cost of $475. Four tumors were identified with this technique. Cost analysis indicates that supplanting ABR with this limited MRI may well represent a cost-effective approach for evaluating patients with suspected retrocochlear lesions.

Cochlea↗
PubMed1996

Distinct domains of hTAFII100 are required for functional interaction with transcription factor TFIIF beta (RAP30) and incorporation into the TFIID complex.

TFIID is the DNA binding component of the RNA polymerase II transcriptional machinery and is composed of the TATA binding protein (TBP) and TBP-associated factors (TAFIIs). Here we report the characterization of a new human TAF, hTAFII100, which is the human homologue of Drosophila TAFII80 and yeast TAFII90. hTAFII100 interacts strongly with hTAFII250, hTAFII55 and hTAFII28, less with hTAFII20 and hTAFII18, weakly with TBP and not at all with delta NTAFII135 and hTAFII30. Deletion analysis revealed that the C-terminal half of hTAFII100, which contains six WD-40 repeats, is not required for incorporation into the TFIID complex. Our results suggest that hTAFII100 can be divided into two domains, the N-terminal region responsible for interactions within the TFIID complex and the C-terminal WD repeat-containing half responsible for interactions between hTAFII100 and other factors. An anti-hTAFII100 antibody, raised against a C-terminal epitope, selectively inhibited basal TFIID-dependent in vitro transcription and the specific interaction between hTAFII100 and the 30 kDa subunit of TFIIF (RAP30). We demonstrate that the hTAFII100-TFIIF interaction supports pre-initiation complex formation in the presence of TFIID. Thus, this is the first demonstration that a TAFII functionally interacts with a basal transcription factor in vitro.

Amino Acid Sequence↗
PubMed1996

The gene (POLR2L) encoding the hRPB7.6 subunit of human RNA polymerase.

The gene (POLR2L) encoding a 7.6-kDa subunit (hRPB7.6) of human RNA polymerase has been cloned. It compromises two exons, 116 and 227 bp, respectively, interspaced with an intron of about 2.1 kb. This gene, whose localization has been assigned to the short arm of chromosome 11 (position 11p15), is transcribed in HeLa cells as one major messenger RNA, which encodes a 67-residue polypeptide (7645 Da) that shares strong homologies with the corresponding subunits of other eukaryotic and archaeal RNA polymerase subunits. Like its yeast counterpart (ABC10 beta, encoded by the RPB10 gene), the hRPB7.6 subunit may be shared by all three classes of human nuclear RNA polymerase. Cysteine residues characteristic of an atypical zinc-binding domain are conserved in the homologous sequences of all six species analyzed. A small, related RNA polymerase subunit from vaccinia virus exhibits an identical set of cysteines, suggesting that these residues may be contribute to a crucial function in the multimeric RNA polymerases.

Amino Acid Sequence↗
PubMed1995

Four subunits that are shared by the three classes of RNA polymerase are functionally interchangeable between Homo sapiens and Saccharomyces cerevisiae.

Four cDNAs encoding human polypeptides hRPB7.0, hRPB7.6, hRPB17, and hRPB14.4 (referred to as Hs10 alpha, Hs10 beta, Hs8, and Hs6, respectively), homologous to the ABC10 alpha, ABC10 beta, ABC14.5, and ABC23 RNA polymerase subunits (referred to as Sc10 alpha, Sc10 beta, Sc8, and Sc6, respectively) of Saccharomyces cerevisiae, were cloned and characterized for their ability to complement defective yeast mutants. Hs10 alpha and the corresponding Sp10 alpha of Schizosaccharomyces pombe can complement an S. cerevisiae mutant (rpc10-delta::HIS3) defective in Sc10 alpha. The peptide sequences are highly conserved in their carboxy-terminal halves, with an invariant motif CX2CX12RCX2CGXR corresponding to a canonical zinc-binding domain. Hs10 beta, Sc10 beta, and the N subunit of archaeal RNA polymerase are homologous. An invariant CX2CGXnCCR motif presumably forms an atypical zinc-binding domain. Hs10 beta, but not the archaeal subunit, complemented an S. cerevisiae mutant (rpb10-delta 1::HIS3) lacking Sc10 beta. Hs8 complemented a yeast mutant (rpb8-delta 1::LYS2) defective in the corresponding Sc8 subunit, although with a strong thermosensitive phenotype. Interspecific complementation also occurred with Hs6 and with the corresponding Dm6 cDNA of Drosophila melanogaster. Hs6 cDNA and the Sp6 cDNA of S. pombe are dosage-dependent suppressors of rpo21-4, a mutation generating a slowly growing yeast defective in the largest subunit of RNA polymerase II. Finally, a doubly chimeric S. cerevisiae strain bearing the Sp6 cDNA and the human Hs10 beta cDNA was also viable. No interspecific complementation was observed for the human hRPB25 (Hs5) homolog of the yeast ABC27 (Sc5) subunit.

Amino Acid Sequence↗
PubMed1995

Eukaryotic GST fusion vector for the study of protein-protein associations in vivo: application to interaction of ATFa with Jun and Fos.

We describe a multipurpose eukaryotic expression vector that incorporates the following features: restriction sites for in-frame insertion of cDNAs of interest between sequences encoding the glutathione-S-transferase (GST) and an oligohistidine element, allowing expression of the corresponding fusion proteins; a phosphorylation site for protein kinase A for in vitro labeling of the fusion protein; a T7 promoter for in vitro transcription and subsequent translation; and signals for single-stranded DNA production in bacteria. We have used this vector to demonstrate the formation in vivo of complexes between the transcription factor ATFa, a member of the family of ATF/CRE binding proteins, and the c-Jun or c-Fos proteins. Such interactions could be detected in crude extracts from cells transfected with vectors expressing the GST-ATFa fusion protein, as well as the c-Jun or c-Fos proteins. Complexes containing both ATFa and either c-Jun or c-Fos were specifically retained on glutathione (GSH)-agarose beads as revealed by immunoblot analyses. We also show that the leucine zipper domain of ATFa is essential for this interaction.

Activating Transcription Factors↗
PubMed1994

Chromosomal localization of human RNA polymerase II subunit genes.

The eukaryotic DNA-dependent RNA polymerase II (or B) is composed of 10 to 14 polypeptides ranging from 220 to 10 kDa. To gain further insight into the molecular structure and function of these subunits, we have undertaken the molecular cloning of nucleotide sequences corresponding to the human enzyme. The cDNAs of five subunits (hRPB220, hRPB140, hRPB33, hRPB25, and hRPB14.5) have been isolated. Using in situ hybridization, we show that the genes of these subunits have distinct chromosomal locations (17p13, 4q12, 16q13-q21, 19p13.3, and 19q12, respectively). Thus, if assembly of active polymerase molecules requires coordinated expression from these independent genes, mechanisms that ensure tight coregulation of the corresponding promoters must exist.

Chromosome Banding↗
PubMed1994

A 14.4 KDa acidic subunit of human RNA polymerase II with a putative leucine-zipper.

The cDNA of a small subunit (hRPB14.4) of RNA polymerase II (or B) from HeLa cells has been cloned. A 127 residue peptide sequence (calculated molecular weight of 14,478; isoelectric point of 3.7) was deduced and compared to that of the homologous subunit of Saccharomyces cerevisiae polymerase (ABC23, encoded by the RPB6/RPO26 gene). About 50% of the total residues were found to be conserved between yeast and man, with the C-terminal two-third being the most conserved (72% identity). A putative leucine-zipper comprising four properly spaced leucine residues, but not preceded by a basic domain, was identified near the C-terminal end of both proteins.

Amino Acid Sequence↗
PubMed1993

Structure of the gene encoding the 14.5 kDa subunit of human RNA polymerase II.

The structure of the gene encoding the 14.5 kDa subunit of the human RNA polymerase II (or B) has been elucidated. The gene consists of six exons, ranging from 52 to over 101 bp, interspaced with five introns ranging from 84 to 246 bp. It is transcribed into three major RNA species, present at low abundance in exponentially growing HeLa cells. The corresponding messenger RNAs contain the same open reading frame encoding a 125 amino acid residue protein, with a calculated molecular weight of 14,523 Da. This protein (named hRPB14.5) shares strong homologies with the homologous polymerase subunits encoded by the Drosophila (RpII15) and yeast (RPB9) genes. Cysteines characteristic of two zinc fingers are conserved in all three corresponding sequences and, like the yeast protein, the hRPB14.5 subunit exhibits zinc-binding activity.

Amino Acid Sequence↗
PubMed1992

Primary structure of the second largest subunit of human RNA polymerase II (or B).

The cDNA of the second largest subunit of RNA polymerase II (or B) from HeLa cells has been cloned and sequenced. A predicted amino acid sequence of 1174 residues (calculated molecular mass of 133,896 Da) was derived from the longest open reading frame and compared to the sequences of homologous subunits of polymerases of eukaryotic, archaeal and bacterial origin. After optimal alignment, about 16% of the residues were found to be conserved throughout evolution, from human to Escherichia coli. About 2/3 of the overall length of the conserved domains delineated by these residues are clustered within the C-terminal half of the human polypeptide, whereas the remaining is spread over its N-terminal half. The putative functional significance of these conserved domains is discussed.

Amino Acid Sequence↗
PubMed1988

Angina and ST-segment depression during treadmill and arm ergometer testing in patients with coronary artery disease.

The clinical use of exercise rehabilitation programs has increased for patients with coronary artery disease. Exercise testing in these programs typically is conducted on a treadmill or cycle ergometer, although many patients' vocations require upper extremity activities and some patients cannot perform lower extremity exercises. To compare the hemodynamic responses and the incidence of angina and ST-segment depression during upper and lower extremity exercise in patients with coronary artery disease, we administered symptom-limited arm ergometer and submaximal or maximal symptom-limited treadmill tests to 95 cardiac rehabilitation patients who had completed an eight-week exercise training program. Treadmill testing resulted in significantly higher heart rates, systolic blood pressures, and double products than arm ergometer testing. The incidence of ST-segment depression was significantly greater with treadmill testing than with arm ergometer testing, but the incidence of angina was not different between tests. Ten patients had ST-segment depression during both arm ergometer and treadmill testing, and the double products at the onset of ST-segment depression were not different. Our data suggest that arm ergometer testing is less likely to result in ST-segment depression than treadmill testing in patients with coronary artery disease, possibly because of the lower hemodynamic responses during arm ergometer testing.

Coronary Disease↗