The interaction of nitrite with photosynthetic electron transport under anaerobic conditions

Chlorella cells were examined in a modulated oxygen polarograph under aerobic and anaerobic conditions. At light intensities below about 600 ergs · cm^?2 · s^?1 of 650 nm light, the oxygen yield and phase lag are lower under anaerobic conditions. Addition of 25 mM sodium nitrite increases both these parameters to values close to those found in the presence of oxygen. It is proposed that nitrite is reduced by Photosystem I thus diverting electrons from the cyclic electron transport pathway. The intersystem electron transport chain becomes more oxidized and this suppresses a backflow of electrons to the oxidizing side of Photosystem II, hence increasing the oxygen yield and the phase lag. The removal of oxygen from the bathing medium also alters the response of dark adapted _Chlorella to a series of saturating light flashes. In terms of the Kok model of Photosystem II (Kok, B., Forbush, B. and McGloin, M. (1970) Photochem. Photobiol. 11, 457–475) there is a large increase in the parameter α. Addition of nitrite reverses this change and virtually restores the response seen in the presence of oxygen. The deactivation of the S₂ state is greatly speeded up in the absence of oxygen but the addition of nitrite again reverses this.     

Expression of a reporter gene interrupted by the Candida albicans group I intron is inhibited by base analogs.

We previously reported the identification of an intron (CaLSU) in the 25S ribosomal RNA of some Candida albicans yeast strains. CaLSU was shown to self-splice and has the potential to adopt a secondary structure typical of group I introns. The presence of CaLSU inC. albicans strains correlates with a high degree of susceptibility to base analog antifungal agents, 5-fluorocytosine (5-FC) or 5-fluorouracil (5-FU). Cell death, resulting from addition of base analogs to growing cultures, precluded demonstration of a causal relationship between CaLSU presence and susceptibility to base analogs. In the present study, CaLSU was inserted in a non-essential lacZ reporter gene and expression was examined in Saccharomyces cerevisiae. Different mutations affecting in vitro self-splicing also had similar effects on reporter gene expression in vivo. This indicates that in vivo removal of CaLSU from the reporter gene occurs through the typical self-splicing mechanism of group I introns. Base analogs inhibited expression of the reporter gene product in a concentration-dependent manner upon their addition to the cultures. This supports a model in which disruption of intron secondary structure, consecutive to the incorporation of nucleotide analogs, is a major factor determining the susceptibility of C.albicans cells to base analogs.     

Defensive behaviour and its inheritance in the anabantoid fish, Macropodus opercularis and Macropodus opercularis concolor

In this preliminary study defense behaviour patterns (fear responses) are described in two closely related, behaviourally different inbred labyrinth fish subspecies and in their F₁ generation. The subspecies M. opercularis (characterized briefly by “active escape”) and M. opercularis concolor (characterized by “passive escape”) showed specific differences in the manifestation of certain defense behaviour patterns. In the F₁ hybrid generation dominance and overdominance of M. opercularis was found in most defense behaviour patterns. Analysing the frequencies and sequences of movement patterns it could be shown that defensive behaviour is not a random or entirely “plastic” process but that there is sequential linkage between the patterns and they form characteristic clusters. Our results suggest that manifestations of different patterns are under genetic control and presumably, genetic determination of certain patterns is not very complex. Attempts were made to determine whole brain noradrenaline, serotonine and dopamine levels of the two subspecies and a significant difference was found in the noradrenaline content.     

Cell Budding from Normal Appearing Epithelia: A Predictor of Colorectal Cancer Metastasis?

Background: Colorectal carcinogenesis is believed to be a multi-stage process that originates with a localized adenoma, which linearly progresses to an intra-mucosal carcinoma, to an invasive lesion, and finally to metastatic cancer. This progression model is supported by tissue culture and animal model studies, but it is difficult to reconcile with several well-established observations, principally among these are that up to 25% of early stage (Stage I/II), node-negative colorectal cancer (CRC) develop distant metastasis, and that circulating CRC cells are undetectable in peripheral blood samples of up to 50% of patients with confirmed metastasis, but more than 30% of patients with no detectable metastasis exhibit such cells. The mechanism responsible for this diverse behavior is unknown, and there are no effective means to identify patients with pending, or who are at high risk for, developing metastatic CRC.Novel findings: Our previous studies of human breast and prostate cancer have shown that cancer invasion arises from the convergence of a tissue injury, the innate immune response to that injury, and the presence of tumor stem cells within tumor capsules at the site of the injury. Focal degeneration of a capsule due to age or disease attracts lymphocyte infiltration that degrades the degenerating capsules resulting in the formation of a focal disruption in the capsule, which selectively favors proliferating or “budding” of the underlying tumor stem cells. Our recent studies suggest that lymphocyte infiltration also triggers metastasis by disrupting the intercellular junctions and surface adhesion molecules within the proliferating cell buds causing their dissociation. Then, lymphocytes and tumor cells are conjoined through membrane fusion to form tumor-lymphocyte chimeras (TLCs) that allows the tumor stem cell to avail itself of the lymphocyte''s natural ability to migrate and breach cell barriers in order to intravasate and to travel to distant organs. Our most recent studies of human CRC have detected nearly identical focal capsule disruptions, lymphocyte infiltration, budding cells, and the formation of TLCs. Our studies have further shown that age- and type-matched node-positive and -negative CRC have a significantly different morphological and immunohistochemical profile and that the majority of lymphatic ducts with disseminated cells are located within the mucosa adjacent to morphologically normal appearing epithelial structures that express a stem cell-related marker.New hypothesis: Based on these findings and the growth patterns of budding cells revealed by double immunohistochemistry, we further hypothesize that metastatic spread is an early event of carcinogenesis and that budding cells overlying focal capsule disruptions represent invasion- and metastasis-initiating cells that follow one of four pathways to progress: (1) to undergo extensive in situ proliferation leading to the formation of tumor nests that subsequently invade the submucosa, (2) to migrate with associated lymphocytes functioning as “seeds” to grow in new sites, (3) to migrate and intravasate into pre-existing vascular structures by forming TLCs, or (4) to intravasate into vascular structures that are generated by the budding cells themselves. We also propose that only node-positive cases harbor stem cells with the potential for multi-lineage differentiation and unique surface markers that permit intravasation.     

RNA profile of blood cells from LSD-affected persons.

This work shows the existence of differences in RNA profiles as obtained from blood cells of two LSD-affected persons. These had received slightly different concentrations of LSD yet their RNA profiles between them, and those of control patients, are remarkably different, especially regarding the 4S peaks. Further work is now being done in our laboratory in order to understand the meaning of these important differences.     

On the Origin of Protein Synthesis Factors: A Gene Duplication/Fusion Model

Sequence similarity has given rise to the proposal that IF-2, EF-G, and EF-Tu are related through a common ancestor. We evaluate this proposition and whether the relationship can be extended to other factors of protein synthesis. Analysis of amino acid sequence similarity gives statistical support for an evolutionary affiliation among IF-1, IF-2, IF-3, EF-Tu, EF-Ts, and EF-G and suggests further that this association is a result of gene duplication/fusion events. In support of this mechanism, the three-dimensional structures of IF-3, EF-Tu, and EF-G display a predictable domain structure and overall conformational similarity. The model that we propose consists of three consecutives duplication/fusion events which would have taken place before the divergence of the three superkingdoms: eubacteria, archaea, and eukaryotes. The root of this protein superfamily tree would be an ancestor of the modern IF-1 gene sequence. The repeated fundamental motif of this protein superfamily is a small RNA binding domain composed of two α-helices packed along side of an antiparallel β-sheet. Received: 17 October 1996 / Accepted: 10 June 1997     

The Ll.LtrB intron from Lactococcus lactis excises as circles in vivo: insights into the group II intron circularization pathway

Group II introns are large ribozymes that require the assistance of intron-encoded or free-standing maturases to splice from their pre-mRNAs in vivo. They mainly splice through the classical branching pathway, being released as RNA lariats. However, group II introns can also splice through secondary pathways like hydrolysis and circularization leading to the release of linear and circular introns, respectively. Here, we assessed in vivo splicing of various constructs of the Ll.LtrB group II intron from the Gram-positive bacterium Lactococcus lactis. The study of excised intron junctions revealed, in addition to branched intron lariats, the presence of perfect end-to-end intron circles and alternatively circularized introns. Removal of the branch point A residue prevented Ll.LtrB excision through the branching pathway but did not hinder intron circle formation. Complete intron RNA circles were found associated with the intron-encoded protein LtrA forming nevertheless inactive RNPs. Traces of double-stranded head-to-tail intron DNA junctions were also detected in L. lactis RNA and nucleic acid extracts. Some intron circles and alternatively circularized introns harbored variable number of non-encoded nucleotides at their splice junction. The presence of mRNA fragments at the splice junction of some intron RNA circles provides insights into the group II intron circularization pathway in bacteria.