Functional Identification of the Hypoxanthine/Guanine Transporters YjcD and YgfQ and the Adenine Transporters PurP and YicO of Escherichia coli K-12

The evolutionarily broad family nucleobase-cation symporter-2 (NCS2) encompasses transporters that are conserved in binding site architecture but diverse in substrate selectivity. Putative purine transporters of this family fall into one of two homology clusters: COG2233, represented by well studied xanthine and/or uric acid permeases, and COG2252, consisting of transporters for adenine, guanine, and/or hypoxanthine that remain unknown with respect to structure-function relationships. We analyzed the COG2252 genes of Escherichia coli K-12 with homology modeling, functional overexpression, and mutagenesis and showed that they encode high affinity permeases for the uptake of adenine (PurP and YicO) or guanine and hypoxanthine (YjcD and YgfQ). The two pairs of paralogs differ clearly in their substrate and ligand preferences. Of 25 putative inhibitors tested, PurP and YicO recognize with low micromolar affinity N⁶-benzoyladenine, 2,6-diaminopurine, and purine, whereas YjcD and YgfQ recognize 1-methylguanine, 8-azaguanine, 6-thioguanine, and 6-mercaptopurine and do not recognize any of the PurP ligands. Furthermore, the permeases PurP and YjcD were subjected to site-directed mutagenesis at highly conserved sites of transmembrane segments 1, 3, 8, 9, and 10, which have been studied also in COG2233 homologs. Residues irreplaceable for uptake activity or crucial for substrate selectivity were found at positions occupied by similar role amino acids in the Escherichia coli xanthine- and uric acid-transporting homologs (XanQ and UacT, respectively) and predicted to be at or around the binding site. Our results support the contention that the distantly related transporters of COG2233 and COG2252 use topologically similar side chain determinants to dictate their function and the distinct purine selectivity profiles.     

Have the bloody cells gone to our heads?

Recent studies have shown that cells expressing neuronal antigens can be derived from a bone marrow transplant. A new report lends support to and extends these previous results by presenting compelling morphological evidence for the generation and integration of highly differentiated bone marrow-derived neurons.     

Electron microscopical studies of Strongyloides ratti infective larvae: loss of the surface coat during skin penetration

Previous indications using radiolabelled larvae that Strongyloides ratti free-living infective larvae lose a surface coat during penetration of the skin were further investigated by transmission electron microscopy of the cuticle of S. ratti infective larvae in the free-living stage, after penetration of mouse skin, and after migration to the lungs. These studies demonstrated the presence of a faint electron-dense surface coat external to the epicuticle on free-living worms which was absent from larvae recovered from the skin and lungs. When free-living infective larvae were incubated in 10% CO2 at 37 C and then examined with phase-contrast microscopy, worms were observed in the process of losing this coat. These observations confirm the hypothesis that S. ratti infective larvae lose a surface coat during penetration of the skin.     

The nuclear DNA content of human breast carcinoma. Associations with clinical stage, axillary lymph node status, estrogen receptor status and outcome

Using Feulgen-DNA cytophotometry, the nuclear DNA content was determined in specimens from 169 female patients with unilateral primary carcinoma of the breast. The tumors were classified as either diploid (73 cases: 43%) or hyperdiploid (96 cases), according to the ploidy of the tumor cells. Statistically significant associations were found between the DNA content and other characteristics of the patients and their tumors. (1) In postmenopausal women, inoperable tumors were more likely to be hyperdiploid (P less than .005). (2) In patients with operable disease, diploid tumors were less likely to have metastasized to the axillary lymph nodes (P less than .005) and were also less likely to have four or more positive nodes (P = .0044). (3) Overall, 71% of the diploid tumors and 52% of the hyperdiploid tumors were estrogen-receptor (ER) positive. This difference in proportions was statistically significant (P less than .05), but when the patients were divided into premenopausal and post-menopausal groups, the proportions of ER-positive tumors were not significantly different in either group. (4) In 113 patients considered suitable for studies on outcome (mean length of follow-up of 27 months, with a range from 0 to 71 months), the rates of relapse were 3 of 55 diploid cases and 17 of 58 hyperdiploid cases. The rate of relapse was higher in the hyperdiploid group, irrespective of lymph node status.     

FINE STRUCTURAL STUDIES ON THE INTERPHASE AND DIVIDING APICAL CELLS OF SPHACELARIA TRIBULOIDES (PHAEOPHYTA)1

The apical cells of Sphacelaria tribuloides Menegh. are larger than other thallus cells, contain more organelles and appear polarized. Their tip portion, where they grow, contains a well developed Golgi apparatus, abundant endoplasmic reticulum (ER) membranes, mitochondria, chloroplasts and a large number of small vacuoles. It seems likely that a continuous flow of membranous material from the ER membranes to the dictyosomes and from the latter to the plasmalemma of the extending tip portion takes place. In contrast, the basal pole possesses fewer organelles and is occupied mainly by large-sized, sometimes central vacuoles. The apical cells undergo two distinct types of highly asymmetrical differential divisions giving rise to cells of the thallus and hair initials. During the early stages of mitosis the nuclear envelope remains intact, except for fenestrated poles. Microtubules pass through the fenestrae into the nucleoplasm. During meta-phase, a typical chromosome plate is organized. The sites of attachment of spindle microtubules to the chromosomes are structurally different from the rest of the chromosomes. At late anaphase, the nuclear envelope breaks down completely. During telophase, a new membrane encloses the chromosomes which are decondensed and the nucleoli are reorganized. Cytokinesis proceeds long after mitosis at a stage in which the nuclei have increased in size and have moved farther apart. A membranous furrow develops centripetally, without the participation of microtubules. However, microtubules traverse the thin cytoplasmic strands which, in both interphase and cytokinetic cells, meander among the vacuoles of the basal pole of the cell and the internuclear space. Dictyosomes appear to be involved in the subsequent wall deposition.     

Clotting Problems with the Teflon-Silastic Arteriovenous Shunt in Patients on Regular Haemodialysis

Episodes of clotting that occurred in 22 patients on regular haemodialysis were studied over a six-month period. The venous pressure during dialysis and the radiology of the Teflon-Silastic arteriovenous shunt were found to be satisfactory guides for the management of the shunt. The failure of the shunt during the early stage was mainly due to technical reasons. Histological study of the excised vessels in removed long-term shunts showed that these had failed because of rigidity and thickening of the vessel wall due to calcium and iron deposits or chronic inflammation, or both.     

Kurzperiodische Schwankungen im Chlorophyllgehalt von Kotyledonen verschiedener Entwicklungsstadien

Zusammenfassung Junge Kotyledonen vonPerilla ocymoides zeigen beim tagesperiodischen Licht-Dunkel-Wechsel während des Ergrünungsprozesses eine Zunahme beider Chlorophylle in der Lichtphase, eine geringe Abnahme während der Dunkelphase. In 12 Std langen Dunkelphasen nimmt dabei das Chlorophyll a um 6%, das Chlorophyll b um 20% (das Gesamtchlorophyll um 9,5%) ab.In etwas älteren Kotyledonen zeigt sich bei 12:12stündigem Licht-Dunkel-Wechsel ein Maximum beider Chlorophylle etwa gegen Mitte der Lichtperiode, ein Minimum etwa gegen Ende der Dunkelperiode. Das Maximum des nächsten Tages erreicht zunächst noch dasjenige des vorhergehenden, liegt aber in noch älteren Kotyledonen noch geringer als dieses.Die Schwankungen im Chlorphyllgehalt laufen zeitlich parallel mit den früher festgestellten Schwankungen in der Fähigkeit zur Chlorophyllbildung.Mit 8 TextabbildungenDem Andenken anFrank Eberhardt.     

Production and function of cytokines in natural and acquired immunity to Candida albicans infection.

Host resistance against infections caused by the yeast Candida albicans is mediated predominantly by polymorphonuclear leukocytes and macrophages. Antigens of Candida stimulate lymphocyte proliferation and cytokine synthesis, and in both humans and mice, these cytokines enhance the candidacidal functions of the phagocytic cells. In systemic candidiasis in mice, cytokine production has been found to be a function of the CD4+ T helper (Th) cells. The Th1 subset of these cells, characterized by the production of gamma interferon and interleukin-2, is associated with macrophage activation and enhanced resistance against reinfection, whereas the Th2 subset, which produces interleukins-4, -6, and -10, is linked to the development of chronic disease. However, other models have generated divergent data. Mucosal infection generally elicits Th1-type cytokine responses and protection from systemic challenge, and identification of cytokine mRNA present in infected tissues of mice that develop mild or severe lesions does not show pure Th1- or Th2-type responses. Furthermore, antigens of C. albicans, mannan in particular, can induce suppressor cells that modulate both specific and nonspecific cellular and humoral immune responses, and there is an emerging body of evidence that molecular mimicry may affect the efficiency of anti-Candida responses within defined genetic contexts.     

AIDS in Africa: distinguishing fact and fiction

The data widely purporting to show the existence and heterosexual transmission in Africa of a new syndrome caused by a retrovirus which induces immune deficiency are critically evaluated. It is concluded that both acquired immune deficiency (AID) and the symptoms and diseases which constitute the clinical syndrome (S) are of long standing in Africa, affect both sexes equally and are caused directly and indirectly by factors other than human immunodeficiency virus (HIV). Seropositivity to HIV in Africans usually represents no more than cross-reactivity caused by an abundance of antibodies induced by the numerous infectious and parasitic diseases which are endemic in Africa. The apparently high prevalence of AIDS and HIV seropositives is therefore not surprising and is not proof of heterosexual transmission of either HIV or AIDS.E. Papadopulos-Eleopulos is with the Department of Medical Physics, The Royal Perth Hospital, Perth 6000, Western Australia, Australia; V.F. Turner is with the Department of Emergency Medicine, The Royal Perth Hospital, Perth 6000, Western Australia, Australia, J.M. Papadimitriou is with the Department of Pathology, University of Western Australia, Perth, Western Australia. H. Bialy is with Bio/Technology, 65 Becker St, New York, NY 10012, USA.     

Lanosterol 14α-demethylase. Similarity of the enzyme system from yeast and rat liver

The chemical synthesis of 24,25-dihydro[32-¹⁴C]lanosterol is described. The incubation of this material with a cell-free system from $\text{Saccharomvoes cerevisiae}$ or with a microsomal preparation from rat liver resulted in both cases in the release of [¹⁴C]formic acid. This result suggests that in the biosynthesis of ergosterol in yeast, as well as in that of cholesterol in higher animals, the 14α-methyl group of lanosterol is removed as formic acid. In both systems, the measurement of the rate of release of [¹⁴C]formic acid from 24,25-dihydro[32-¹⁴C]lanosterol provides a simple and direct assay of lanosterol 14α-demethylase. Carbon monoxide inhibited both yeast and liver 14α-demethylase.