Conformations of deoxydinucleoside phosphates containing pyrimidine-pyrimidine photodimers

Conformational analysis of deoxydinucleoside monophosphates with the sequences TpT and CpC have been carried out with the incorporation of both cyclobutane type pyrimidine dimers and 6-4 photoadducts using the methods of molecular mechanics energy minimization. The effect of flexibility with respect to sugar geometries and glycosidic torsions have been studied and the relative energies of a large variety of structures have been compared. The salient features obtained from these calculations have been compared with the crystallographic and spectroscopic data on pyrimidine dimer incorporated deoxydinucleoside monophosphates. Effects of "inserting" the energetically favourable conformations of such structures into B-DNA helices have been discussed in terms of the distortions in helical structures.     

Purification and properties of glutamyl aminopeptidase from chicken egg-white

Hydrolytic activities characteristic for different aminopeptidases were detected in the egg-white of unfertilized chicken eggs, and one aminopeptidase was isolated in an electrophoretically homogeneous form. The isolated aminopeptidase preferentially hydrolyzed bonds of alpha-glutamyl residue at the NH(2)-end of synthetic substrates and peptides. The enzyme is a dimer with an M(r) of 320,000 and pI of 4.2. Its optimal pH and temperature are 7.6 and 60 degrees C, respectively. EDTA, amastatin, and N-bromosuccinimide are inhibitors, while Ca2++ and Mn2+ are activators of the enzyme Ca2+ also stabilizes the enzyme. According to the observed properties, the isolated chicken egg-white aminopeptidase belongs to the glutamyl aminopeptidases.     

Infectivity inhibition of HIV prototype strains by antibodies directed against a peptide sequence of mycoplasma

Antibodies prepared against a peptide corresponding to the site of cyto-adherence of Mycoplasma genitalium adhesine inhibit or reduce the infectivity of the HIV-1BRU and HIV-2ROD strains of Human Immunodeficiency Virus in lymphoid cells. These results strengthen the hypothesis that some mycoplasmas may play an important part in HIV replication and pathogenicity.     

Isolation and chromosomal localization of the human glutathione peroxidase gene

We have isolated cDNA clones for the gene, termed GPX1, encoding the major human selenoprotein, glutathione peroxidase. Sequence analysis confirmed previous findings that the unusual amino acid seleno-cysteine is encoded by the opal terminator codon UGA. Southern blot analysis of human genomic DNA with the GPX1 cDNA showed that restriction endonucleases without sites in the probe sequence produced three hybridizing bands at standard stringency, diminishing to one strongly and one weakly hybridizing band at high stringency. In situ hybridization localized the human GPX1 gene to a single site on chromosome 3, at region 3q11-13.1. Thus, three genomic sites bear sequence homology to the GPX1 cDNA, and the one most homologous maps to 3q11-13.1.     

Neuron-specific and state-specific differences in calcium homeostasis regulate the generation and degeneration of neuronal architecture

Many stimuli (e.g., neurotransmitters and electrical activity) regulate neuromorphogenesis by changing intracellular calcium. The ionophore A23187 was employed as a receptor-independent method to investigate neuronal calcium homeostasis. Distinctive neuron-specific (B5 versus B19) and state-specific (growing versus non-growing) differences in calcium homeostasis were observed in cultured identified Helisoma neurons. Fura-2 studies revealed that A23187 induced a transient rise in intracellular calcium in growing neurons B5 but a sustained rise in growing neurons B19. In stable-state (non-growing) cells A23187 evoked only a transient calcium rise. Both neuron-specific and state-specific differences in calcium homeostasis were dependent on extracellular sodium. Morphological studies also indicated that such differences in calcium-regulatory capacity can have profound consequences on the generation and degeneration of neuronal architecture.     

Dynamic changes in optic fiber terminal arbors lead to retinotopic map formation: an in vivo confocal microscopic study

Dynamic remodeling of retinal ganglion cell terminal arbors has been proposed to contribute to formation of the topographically ordered retinotectal projection. To test this directly, the growth of individual terminal arbors was observed in live X. laevis tadpoles using a confocal microscope to visualize their complex three-dimensional structure. During initial development, nasal and temporal retinal arbors covered overlapping tectal areas. Despite subsequent remodeling, the dimensions and positions of the temporal arbors remained relatively stable. In contrast, the nasal arbors grew caudally, as they extended caudal branches and retracted rostral branches. These results suggest that differences in the remodeling of the nasal and temporal arbors lead to the emergence of retino-topography along the rostrocaudal axis of the tectum. All the terminal arbors were dynamic, including those with stable dimensions, suggesting that continual remodeling of arbors may be a universal feature of neuronal projections.