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Summary Diatoms contain a highly flexible capacity to dissipate excessively absorbed light by nonphotochemical fluorescence quenching (NPQ) based on the light-induced conversion of diadinoxanthin (Dd) into diatoxanthin (Dt) and the presence of Lhcx proteins. Their NPQ fine regulation on the molecular level upon a shift to dynamic light conditions is unknown. We investigated the regulation of Dd + Dt amount, Lhcx gene and protein synthesis and NPQ capacity in the diatom Phaeodactylum tricornutum after a change from continuous low light to 3 d of sine (SL) or fluctuating (FL) light conditions. Four P. tricornutum strains with different NPQ capacities due to different expression of Lhcx1 were included. All strains responded to dynamic light comparably, independently of initial NPQ capacity. During SL, NPQ capacity was strongly enhanced due to a gradual increase of Lhcx2 and Dd + Dt amount. During FL, cells enhanced their NPQ capacity on the first day due to increased Dd + Dt, Lhcx2 and Lhcx3; already by the second day light acclimation was accomplished. While quenching efficiency of Dt was strongly lowered during SL conditions, it remained high throughout the whole FL exposure. Our results highlight a more balanced and cost-effective photoacclimation strategy of P. tricornutum under FL than under SL conditions.

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Diatoms play a crucial role in the biochemistry and ecology of most aquatic ecosystems, especially because of their high photosynthetic productivity. They often have to cope with a fluctuating light climate and a punctuated exposure to excess light, which can be harmful for photosynthesis. To gain insight into the regulation of photosynthesis in diatoms, we generated and studied mutants of the diatom Phaeodactylum tricornutum Bohlin carrying functionally altered versions of the plastidic psbA gene encoding the D1 protein of the PSII reaction center (PSII RC). All analyzed mutants feature an amino acid substitution in the vicinity of the QB -binding pocket of D1. We characterized the photosynthetic capacity of the mutants in comparison to wildtype cells, focusing on the way they regulate their photochemistry as a function of light intensity. The results show that the mutations resulted in constitutive changes of PSII electron transport rates. The extent of the impairment varies between mutants depending on the proximity of the mutation to the QB -binding pocket and/or to the nonheme iron within the PSII RC. The effects of the mutations described here for P. tricornutum are similar to effects in cyanobacteria and green microalgae, emphasizing the conservation of the D1 protein structure among photosynthetic organisms of different evolutionary origins.

Diatoms play a crucial role in the biochemistry and ecology of most aquatic ecosystems, especially because of their high photosynthetic productivity. They often have to cope with a fluctuating light climate and a punctuated exposure to excess light, which can be harmful for photosynthesis. To gain insight into the regulation of photosynthesis in diatoms, we generated and studied mutants of the diatom Phaeodactylum tricornutum Bohlin carrying functionally altered versions of the plastidic psbA gene encoding the D1 protein of the PSII reaction center (PSII RC). All analyzed mutants feature an amino acid substitution in the vicinity of the QB -binding pocket of D1. We characterized the photosynthetic capacity of the mutants in comparison to wildtype cells, focusing on the way they regulate their photochemistry as a function of light intensity. The results show that the mutations resulted in constitutive changes of PSII electron transport rates. The extent of the impairment varies between mutants depending on the proximity of the mutation to the QB -binding pocket and/or to the nonheme iron within the PSII RC. The effects of the mutations described here for P. tricornutum are similar to effects in cyanobacteria and green microalgae, emphasizing the conservation of the D1 protein structure among photosynthetic organisms of different evolutionary origins.

Signal transducer and transcriptional activator (STAT) proteins are latent cytoplasmic transcription factors that are activated in response to stimulation by various cytokines. Protein Inhibitors of Activated STAT (PIAS) proteins comprise a family of five mammalian proteins which have been identified as potentially important downregulators of the STAT signaling pathway. We have previously reported the identification and expression of the mouse homologue of PIAS family member PIASgamma. Here we report the isolation by genomic 5'-RACE PCR and in vitro analysis of the mouse PIASgamma promoter region and the genomic structure and organization of the mouse and human PIASgamma genes. Human PIASgamma spans approximately 23 kb on chromosome 19 and is organized into ten exons. The size of mouse PIASgamma is 16 kb and also organized into ten exons with the intron/exon structure of the two genes conserved in both species. As a result, considerable conservatism of the mouse and human intron sequences was observed. Analysis of a 1.4 kb genomic fragment containing the mouse PIASgamma promoter allowed us to map the transcription 'Start' site of the gene, determine the sequences essential for the activity of this promoter and to define a minimal promoter region.

Signal transducer and activator of transcription (STAT) proteins are latent cytoplasmic transcription factors that become activated in response to stimulation by various cytokines. Recently a new family of five structurally related proteins, called PIAS (Protein Inhibitor of Activated STAT) has been identified as potentially important downregulators of this pathway. Members of the PIAS family of STAT inhibitors may play a prominent role in the downregulation of STAT-mediated signaling processes. In this article we describe the isolation of the cDNA and expression of the gene for the murine homologue of the human STAT inhibitor family member PIASgamma. The cDNA for mPIASgamma encodes a protein of 507 amino acids that is highly homologous to the human protein and is expressed in the mouse as early as d 7.5 of gestation. In situ hybridizations of staged mouse embryos localized the transcript for the PIASgamma gene to the limbs, neuroepithelium, and the inner root sheath of the hair follicle, suggesting a role in the development of these structures. Immunostaining studies with a polyclonal antibody (PAb) recognizing human PIASgamma localized the protein in the hair follicle of human scalp hair and in monkey neuronal cells. Thus PIASgamma exhibits a highly selective pattern of expression, suggesting that it modulates the response of cells to developmental cues.

Research suggests that women low in rape myth acceptance (RMA) perceive sexual violence at an intergroup level (as a threat by all men against all women), whereas women high in RMA perceive sexual violence at an interpersonal level (as an interaction of certain individuals; Bohner, Weisbrod, Raymond, Barzvi, & Schwarz, 1993). Extending this reasoning, we hypothesized that the gender category would generally be more chronically accessible to low RMA women than high-RMA women. In three studies, spontaneous gender-related responses were recorded. In Study 1, 46 female students provided open-ended self-descriptions in response to the question `Who am I?' In Study 2, 51 female users of a public library judged pairs of two women and of a woman and a man for similarity. In Study 3, 48 female students completed word fragments; critical items had both gender-related and neutral solutions. Towards the end of each study, participants' RMA was assessed. As predicted, low-RMA (versus high-RMA) participants were more likely to spontaneously refer to being a woman in their self-descriptions (Study 1), judged `woman-man pairs' as less similar than a `woman-woman pair' (Study 2), and created female gender-related word-completions both faster and more frequently (Study 3).

In diatoms, the process of energy-dependent chlorophyll fluorescence quenching (qE) has an important role in photoprotection. Three components are essential for qE: (1) the light-dependent generation of a transthylakoidal proton gradient; (2) the deepoxidation of the xanthophyll diadinoxanthin (Dd) into diatoxanthin (Dt); and (3) specific nucleus-encoded antenna proteins, called Light Harvesting Complex Protein X (LHCX). We used the model diatom Phaeodactylum tricornutum to investigate the concerted light acclimation response of the qE key components LHCX, proton gradient, and xanthophyll cycle pigments (Dd+Dt) and to identify the intracellular light-responsive trigger. At high-light exposure, the up-regulation of three of the LHCX genes and the de novo synthesis of Dd+Dt led to a pronounced rise of qE. By inhibiting either the conversion of Dd to Dt or the translation of LHCX genes, qE amplification was abolished and the diatom cells suffered from stronger photoinhibition. Artificial modification of the redox state of the plastoquinone (PQ) pool via 3-(3,4-dichlorophenyl)-1,1-dimethylurea and 5-dibromo-6-isopropyl-3-methyl-1,4-benzoquinone resulted in a disturbance of Dd+Dt synthesis in an opposite way. Moreover, we could increase the transcription of two of the four LHCX genes under low-light conditions by reducing the PQ pool using 5-dibromo-6-isopropyl-3-methyl-1,4-benzoquinone. Altogether, our results underline the central role of the redox state of the PQ pool in the light acclimation of diatoms. Additionally, they emphasize strong evidence for the existence of a plastid-to-nucleus retrograde signaling mechanism in an organism with plastids that derived from secondary endosymbiosis.

The structures of the polysaccharide part of lipopolysaccharides isolated from eight Escherichia coli K12/Shigella dysenteriae type 1 hybrids have been determined using sugar and methylation analysis plus 1H- and 13C-nuclear magnetic resonance spectroscopy. The hybrids express parts of the S. dysenteriae type 1 O-antigen tetrasaccharide repeating unit because of the presence of pSS3, a plasmid expressing an alpha-galactosyl: lipopolysaccharide transferase and pSS9, a pBR322 plasmid expressing S. dysenteriae type 1 rfb genes. The various classes of hybrids are the result of transposon Tn 1000 insertions in pSS9 inactivating different rfb genes. The following structural elements were found. E. coli K12 (pSS3) and E. coli K12 (pSS3, pSS9-6; a class I hybrid); alpha-D-Galp(1--3)beta-D-GlcpNAc(1--. Class IV hybrids: E. coli K12 (pSS3, pSS9-36); (pSS3, pSS9-107) and (pSS3, pSS9-114); alpha-L-Rhap(1--2)alpha-D-Galp(1--3)beta-D-GlcpNAc(1--. Class V hybrids: E. coli K12 (pSS3, pSS9-78) and (pSS3, pSS9-111); alpha-L-Rhap(1--3)alpha-L-Rhap(1--2)alpha-D-Galp(1--3)bet a-D-GlcpNAc(1--. The structural sequences are identical to those found in the lipopolysaccharide from native S. dysenteriae type 1. In the hybrid strains, the terminal non-reducing GlcNAc residue of the E. coli K12 core is fully substituted by S. dysenteriae type 1 repeating units, or parts thereof.

Men's rape myth acceptance (RMA; prejudiced beliefs that serve to exonerate the rapist and blame the victim) has been shown to correlate positively with self-reported rape proclivity (RP). To explore the causal pathway underlying this correlation, two experiments were conducted in which the relative cognitive accessibility of RMA and RP was varied. Male students were asked to report their RP in the context of a scale assessing attraction toward sexual aggression (Experiment 1) or in response to five realistic date-rape scenarios (Experiment 2), either before or after they filled out a 20-item RMA scale. In both studies, the correlation of RMA and RP was significantly greater in the after than in the before condition, suggesting that the belief in rape myths has a causal influence on men's proclivity to rape. © 1998 John Wiley & Sons, Ltd.

The in vivo fate of amphotropic murine leukemia retrovirus was studied in five rhesus monkeys. Retrovirus infused intravenously into 3 normal animals and 1 immunosuppressed animal was cleared rapidly from the circulation and subsequent viremia has not been detected (mean follow-up of 27.4 months). A fifth monkey was immunosuppressed and transplanted with virus-producing autologous fibroblasts in addition to an intraperitoneal injection of virus. This animal was viremic for 2 days and its lymph node cells and peripheral blood mononuclear cells were shown to be producing virus for up to 22 days post-inoculation, but subsequently has been negative after 17.0 months of analysis. In the 5 animals studied (combined mean follow-up of 25.7 months), clinical illness has not been identified at any time. Therefore, murine amphotropic retroviruses do not appear to pose an acute health risk.

SUMMARYTwenty t haplotypes were extracted from wild mice captured at several locations in Europe, Israel, North Africa, and South America. The haplotypes were designated tTuw1 through tTuw20. The H-2 haplotypes of the lines were defined using antisera and monoclonal antibodies specific for private antigenic determinants controlled by known H-2 alleles and by antisera produced using the new t lines as donors. The tTuw haplotypes fall into four groups according to the H-2 haplotype associated with them. Haplotypes tTuw10 through tTuw18 are associated with H-2W30, previously found to be linked with haplotypes of the tw1 group. Haplotypes tTuw1 through tTuw6 are associated with a new H-2 haplotype, H-2w36, characterized by the determinant H-2.107. Haplotypes tTuw7 through tTuw9 are associated with another new H-2 haplotype, H-2w37, characterized by determinants H-2.108 and H-2.111. And finally, haplotypes tTuw19 and tTuw20 are associated with yet another new H-2 haplotype, H-2w38, characterized by determinants H-2.33 and H-2.109. These findings suggest that the t polymorphism might be more extensive and more intricate than it was previously thought to be and that at least some of the t-associated H-2 haplotypes, and probably also the t haplotypes themselves, are related to one another in their origin.

Diatoms are a major group of primary producers ubiquitous in all aquatic ecosystems. To protect themselves from photooxidative damage in a fluctuating light climate potentially punctuated with regular excess light exposures, diatoms have developed several photoprotective mechanisms. The xanthophyll cycle (XC) dependent non-photochemical chlorophyll fluorescence quenching (NPQ) is one of the most important photoprotective processes that rapidly regulate photosynthesis in diatoms. NPQ depends on the conversion of diadinoxanthin (DD) into diatoxanthin (DT) by the violaxanthin de-epoxidase (VDE), also called DD de-epoxidase (DDE). To study the role of DDE in controlling NPQ, we generated transformants of P. tricornutum in which the gene (Vde/Dde) encoding for DDE was silenced. RNA interference was induced by genetic transformation of the cells with plasmids containing either short (198 bp) or long (523 bp) antisense (AS) fragments or, alternatively, with a plasmid mediating the expression of a self-complementary hairpin-like construct (inverted repeat, IR). The silencing approaches generated diatom transformants with a phenotype clearly distinguishable from wildtype (WT) cells, i.e. a lower degree as well as slower kinetics of both DD de-epoxidation and NPQ induction. Real-time PCR based quantification of Dde transcripts revealed differences in transcript levels between AS transformants and WT cells but also between AS and IR transformants, suggesting the possible presence of two different gene silencing mediating mechanisms. This was confirmed by the differential effect of the light intensity on the respective silencing efficiency of both types of transformants. The characterization of the transformants strengthened some of the specific features of the XC and NPQ and confirmed the most recent mechanistic model of the DT/NPQ relationship in diatoms.