Pneumocystis carinii shows DNA homology with the ustomycetous red yeast fungi

Pneumocystis carinii causes life-threatening pneumonia in T-lymphocyte-immunodeficient subjects in transplant and oncology units or with acquired immune deficiency syndrome (AIDS). Recent DNA homology studies show P. carinii to be a fungus. To investigate the biology and epidemiology of this parasite further, we elected to determine for it a more precise taxonomic assignment within the fungal kingdom. We screened a wide range of organisms representing the major orders of fungi using DNA amplification and subsequently sequenced a portion of the mitochondrial gene encoding the large subunit ribosomal RNA. Our data show that the opportunistic pulmonary pathogen P. carinii is closely related to the ustomycetous red yeast fungi, a group which includes organisms that are extensively distributed throughout the environment and which release many widely dispersed airborne spores.     

Organization of tyrosine hydroxylase-immunoreactive neurons in the di-and mesencephalon of the American bullfrog (Rana catesbeiana) during metamorphosis

Summary We examined the immunocytochemical distribution of tyrosine hydroxylase, the rate-limiting enzyme in catecholamine synthesis, in the di-and mesencephalon of developing bullfrog tadpoles. Special attention was given to catecholaminergic innervation of the median eminence and pituitary. In premetamorphic tadpoles, tyrosine hydroxylase-immunoreactive neurons were visualized in the suprachiasmatic and infundibular hypothalamus, the ventral thalamus, and midbrain tegmentum by Taylor-Kollros stage V. The number of labeled neurons in all these areas increased as metamorphosis progressed. By mid-prometamorphosis, labeled neurons appeared in the preoptic recess organ as well as in the posterior thalamic nucleus. The majority of cells in the preoptic recess organ, as well as occasional neurons in the suprachiasmatic nucleus, exhibited labeled processes which projected through the ependymal lining of the preoptic recess to contact cerebrospinal fluid. The modified CSF-contacting neurons of the nucleus of the periventricular organ were devoid of specific staining. By late prometamorphosis, labeled fibers from the suprachiasmatic nucleus were observed projecting caudally to enter the hypothalamo-hypophysial-tract en route to innervating the median eminence and pituitary. Labeled fibers arising from the dorsal infundibular nucleus projected ventrolaterally to contribute to catecholaminergic innervation of the median eminence and pituitary. Immunoperoxidase staining of tyrosine hydroxylase-immunoreactive fibers and terminal arborizations in the median eminence were restricted to non-ependymal layers, while labeled fibers in the pituitary were observed in the pars intermedia and pars nervosa. Staining of tyrosine hydroxylase-immunoreactive fibers in the median eminence and pituitary was sparse or absent in premetamorphic tadpoles, but became increasingly more intense as metamorphosis progressed.     

Purification of ribulose 1,5-bisphosphate carboxylase/oxygenase and of carboxysomes from Thiobacillus thyasiris the putative symbiont of Thyasira flexuosa (Montagu)

The bacterial symbionts of many marine invertebrates contain ribulose 1,5-bisphosphate (RuBP) carboxylase but apparently no carboxysomes, polyhedral bodies containing RuBP carboxylase. In the few cases where polyhedral bodies have been observed they have not been characterised enzymatically. Polyhedral bodies, 50–90 nm in diameter, were observed in thin cell sections of Thiobacillus thyasiris the putative symbiont of Thyasira flexuosa and RuBP carboxylase activity was detected in both soluble and particulate fractions after centrifugation of cell-free extracts. RuBP carboxylase purified 90-fold from the soluble fraction was of high molecular weight and consisted of large and small subunits, with molecular weights of 53,110 and 11,100 respectively. Particulate RuBP carboxylase activity was associated with polyhedral bodies 50–100 nm in diameter, as revealed by density gradient centrifugation and electron microscopy. Therefore, the polyhedral bodies were inferred to be carboxysomes. Native electrophoresis of isolated carboxysomes demonstrated a major band which comigrated with the purified RuBP carboxylase and three minor bands of lower molecular weight. Sodium dodecyl-sulphate (SDS) gel electrophoresis of SDS-dissociated carboxysomes demonstrated nine major polypeptides two of which were the large and small subunits of RuBP carboxylase. The RuBP carboxylase subunits represented 21% of the total carboxysomal protein. The most abundant polypeptide had a molecular weight of 40,500. Knowledge of carboxysome composition is necessary to provide an understanding of carboxysome function.Abbreviations FPLC fast performance liquid chromatography - IB isolation buffer - PAGE polyacrylamide gel electrophoresis - RuBP carboxylase - ribulose 1,5-bisphosphate carboxylase/oxygenase - SDS sodium dodecyl-sulphate     

Effect of calcium ion uptake on Candida albicans morphology

In liquid culture using a synthetic medium, added magnesium but not calcium was required for exponential growth of Candida albicans yeast cells. However, medium without added divalent cations supported 2-3 generations of yeast growth or germ tube induction. The addition of calcium ions (1.0 mM) at any stage during the induction of germ tube formation caused reversion to a yeast mode of growth, in contrast to the effect of zinc and cobalt ions which were toxic to all growth. Inhibition of germ tube formation by calcium was not observed in the presence of either magnesium (10 microM) or manganese (100 microM). The presence of either of these ions caused inhibition of 45Ca uptake in yeast cultures. We conclude that unrestricted calcium uptake resulted in the specific inhibition of C. albicans mycelial growth, indicating a critical role for calcium in the regulation of C. albicans morphogenesis.     

Reactivity and fate of benzene and formaldehyde in culture medium with and without fetal calf serum; relevance to in vitro mutagenicity testing

Gas chromatographic-mass spectrometric analyses were performed to determine the reactivity and fate of benzene (BEN) and formaldehyde (FA) in culture medium. BEN (solubility in water: 500 ppm) does not react with culture medium, either with or without fetal calf serum, but its volatility, even in closed vials, is so great that 90% of a 250-ppm solution is lost to the head space after 1 h at 24°C. FA, as a 37% aqueous solution, is a complex mixture that changes composition after 15-min incubation at 38°C. FA is extremely reactive in culture medium containing fetal calf serum, and is much less reactive with medium components in the absence of serum. There is a dramatic increase in the number of daughter products in FA-treated medium over time, such that those seen immediately after FA is added to medium have been replaced after 60-min incubation (38°C in closed vials) by many other interaction products. Methods ensuring maximum solubilization and minimal volatilization of BEN during exposure are essential for obtaining reproducible data on the mutagenic potential of BEN. The volatilization of FA from stock formalin solutions, and, more importantly, the interaction product(s) formed by this highly reactive compound with medium components, especially those in serum, are probably the critical aspects of an effective testing protocol for FA.     

Cellular retinoic acid-binding protein and its relationship to the biological activity of four synthetic retinoids in hamster tracheal organ culture

Summary The mechanism of action of retinoid in reversing keratinization in hamster trachea is yet unknown. The purpose of this study was to determine if cellular retinoic acid binding protein (CRABP) is present in tracheal epithelium following incubation in serum-free, vitamin A-deficient culture medium for 10 days, and if the effectiveness of a retinoid in reversing keratinization in organ culture is correlated with its ability to compete for CRABP sites. The cytosol prepared from tracheal cultures contained CRABP at a concentration of 2.61 pmoles per mg protein. Of the four retinoids with carboxyl end group selected for the study, two of the biological active retinoids competed for the CRABP sites. However, no correlation was observed between the biological activity of the inactive retinoids and their ability to associate with the CRABP sites. These results indicate that even though the action of retinoid may be mediated by retinoid binding protein, it cannot be used as a sole predicator of retinoid response in hamster trachea. This investigation was supported by Contract N01-CP-31012 and U. S. P. H. Grants CA30512 and CA32428, which were awarded by the Division of Cancer Etiology, National Cancer Institute, DHHS. Editor's Statement Tracheal organ cultures provide a useful model for the study of epithelial differentiation and carcinogenesis. Much attention has been given to the action of retinoids in this process. Mehta et al. demonstrate a lack of correlation between biological activity and specific cytosolic binding of members of this class of compounds, pointing out the need for a more complete biochemical understanding of the mechanism of action and active forms of retinoids in this and other systems in vivo and in vitro. David W. Barnes     

Evidence for titratable gating charges controlling the voltage dependence of the outer mitochondrial membrane channel,VDAC

Summary A voltage-dependent anion-selective channel, VDAC, is found in outer mitochondrial membranes. VDAC's conductance is known to decrease as the transmembrane voltage is increased in either the positive or negative direction. Charged groups on the channel may be responsible for this voltage dependence by allowing the channel to respond to an applied electric field. If so, then neutralization of these charges would eliminate the voltage dependence. Channels in planar lipid bilayers which behaved normally at pH 6 lost much of their voltage dependence at high pH. Raising the pH reduced the steepness of the voltage dependence and raised the voltage needed to close half the channels. In contrast, the energy difference between the open and closed state in the absence of a field was changed very little by the elevated pH. The groups being titrated had an apparent pK of 10.6. From the pK and chemical modification, lysine epsilon amino groups are the most likely candidates responsible for VDAC's ability to respond to an applied electric field.     

Effect of a lexA41(Ts) mutation on DNA repair in recA(Def) derivatives of Escherichia coli K-12

Summary Derivatives of Escherichia coli K-12 carrying a deletion of the recA gene survive exposure to UV (254 nm) better if they also contain the lexA41 mutation which codes for a labile LexA protein. This effect of the lexA41 mutation is not observed in comparable strains carrying a uvr A6 mutation. Using two independent methods to detect pyrimidine dimers we found that UV irradiated RecA deficient cells removed dimers from their DNA more rapidly if they contained the lexA41 mutation than if the contained the wild-type lexA gene. Our results are consistent with the idea that a relatively high level of UvrABC incision nuclease resulting from inefficient repression of the corresponding genes by the labile LexA41 protein facilitates excision of pyrimidine dimers from the DNA of UV irradiated cells.