mRNA:guanine-N7 cap methyltransferases: identification of novel members of the family, evolutionary analysis, homology modeling, and analysis of sequence-structure-function relationships

Background  

The 5'-terminal cap structure plays an important role in many aspects of mRNA metabolism. Capping enzymes encoded by viruses and pathogenic fungi are attractive targets for specific inhibitors. There is a large body of experimental data on viral and cellular methyltransferases (MTases) that carry out guanine-N7 (cap 0) methylation, including results of extensive mutagenesis. However, a crystal structure is not available and cap 0 MTases are too diverged from other MTases of known structure to allow straightforward homology-based interpretation of these data.     

An ultrastructural study of the melanophages in the cerebrospinal fluid of the tadpoles of Xenopus

Melanin deposits in the brain ventricles of Xenopus tadpoles were studied with light and electron microscopy (TEM and SEM). They appeared to be aggregations of melanophages which accumulated free pigment granules excreted by ependymal cells into the cerebrospinal fluid. Whereas the meningeal melanophores contained oval melanosomes of various sizes, the melanosomes in the scavenger cells were all spherical, large (0.6–1.1 μm) and fairly uniform in size. Moreover, they were arranged in spherical groups which were never seen in the cytoplasm of the melanophores. The melanosomes within the cells were identical to the free melanosomes found in the cerebrospinal fluid and those which occurred within the ependymal cells in the young larva, suggesting a common origin from the egg cytoplasm. The number of the melanosomes in the melanophages increased with age. Fine cytoplasmic projections were involved in catching and engulfing the melanosomes. Some other features of the cytoplasm, e.g., large deposits of cell detritus, also indicated that the cells were macrophages. In the later stages, (48, 49) no projections were observed, but the cells were totally filled with melanosomes.     

Reexamination of the Byczkowska-Smyk gill surface area data for European teleosts, with new measurements on the pikeperch, Sander lucioperca

This paper reexamines the gill morphometrics of 20 European teleosts first reported in the early gill literature by Byczkowska-Smyk and colleagues in attempt to clarify the long-recognized discrepancies between these data and those obtained in subsequent works. Determination of gill dimensions for the pikeperch, Sander lucioperca, in this study (a species for which Byczkowska-Smyk reported data), along with a literature review for other European teleosts, reveals inaccurate estimation of the total gill surface area by up to 18× for 19 of the 20 species reexamined. This error results primarily from imprecise determination of the bilateral surface area of individual gill lamellae and, to a lesser extent, the incorrect assumption that lamellar area and frequency are species-specific constants that do not vary with fish body mass. This review compiles gill morphometric data from various sources to be used in place of the inaccurate gill area estimates of Byczkowska-Smyk and colleagues and thereby clears the way for higher resolution in the comparative analysis of gill morphology and its correlation to fish habitat and life history characteristics.     

Cloning and expression of Thiobacillus versutus aspartate-semialdehyde dehydrogenase gene in Escherichia coli

The Thiobacillus versutus asd gene coding for aspartate-semialdehyde dehydrogenase was cloned in Escherichia coli cells using pBR322 as a vector. The gene was expressed independently of its orientation, suggesting that E. coli RNA polymerase recognized T. versutus promoter sequence. The T. versutus DNA coded protein, of the molecular weight 44,000, was identified by the analysis of the proteins produced by minicells.     

SEM analysis of dental enamel morphological structures on the basis of their replicas in patients with systemic calcium deficiency

The aim of the present study is to examine microscopically the surface of dental enamel by using a scanning electron microscope (SEM), using their replicas formed in female patients with diagnosed periodontal diseases and systemic calcium deficiency. Replicas of dental enamel surfaces in patients referred for treatment of periodontal diseases were subjected to microscopic analysis. The replicas, after coating with platinum-palladium alloy, were examined under the scanning electron microscope at magnifications of 15–5000 x. Densitometric examinations of spine (L₂ - L₄ segment) revealed bone mineral density BMD T-score lower than −2.5 in 5 patients, in the range of −1.5 to −2.5 in 10 patients, and higher than −1.5 in the remaining patients. Non-homogenous images of surfaces in the form of light and dark areas were observed. Light areas corresponded to damaged surfaces of dental tissues. Patients with higher systemic calcium deficiency had areas lighter in color. More of these areas were found in patients with higher systemic calcium deficiency. It can be assumed that the calcium deficit is likely to appear in the selected dental tissues, particularly in the dental enamel.     

Synthesis and tumoricidal activity of water soluble porphyrinyl-thymidines and related porphyrins

The new cobalt(II)meso-5,10-di(N-methyl-4-pyridinium)-15,20-di(p-phenylene-5′-O-thymidine)porphyrin suppressed the growth of human malignant melanoma cells (M21-HPB) by 95 percent when applied as 2.5 x 10⁻⁵ M solution in tris for 3 days without exposure to light. It was the most effective of the investigated porphyrinyl-nucleosides.     

Temporary Changes in the dc ElectricalConductivity of MX (3-Chloro-4(Dichloromethyl)-5-Hydroxy-2(5H)-Furanone) Treated Collagen

The influence of MX(3-Chloro-4(Dichloromethyl)-5-Hydroxy-2(5H)- Furanone), a stronglymutagenic compound, on the temperature dependence of the dcelectrical conductivity of collagen as a function of time was studied.Collagen was immersed in MX solution, next dried and pressed intotablets. The MX concentration was measured by HPLC analysis.The reduction of MX concentration to 10% of the initial value wasobserved in the presence of collagen in the solution, whereas in thecontrol solution concentration of MX decreased to 70% of the initialvalue. Measurements of electrical conductivity were performed for thetemperature range 295–453K and activation energies for the chargeconduction process were calculated. Within the temperature range295–340K, the presence of MX decreased electrical conductivity ofcollagen. Calculated activation energies were typical for dry proteins.Within the temperature range 295–320K activation energy decreasedwith time, probably due to the stronger interactions in thecollagen-water-MX system. For temperatures between 320–410 and430–450K the activation energy was not time dependent and theapplication of MX did not change the structure of the collagenmacromolecule. The temporary changes occurring at the lowertemperatures being due solely to changes in the collagen-waterinteractions.     

Cloning and expression of Thiobacillus versutus cryptic plasmid pTAV-1 DNA in Escherichia coli

pTAV-1 is an approximately 100 kb Thiobacillus versutus cryptic plasmid. pTAV-1 DNA was cloned in Escherichia coli. Nine recombinant plasmids containing pTAV-1 DNA inserted into the EcoRI restriction site of pACYC184 were constructed. The origin of DNA inserts was confirmed by Southern blot hybridization. The expression of mixotrophic T. versutus plasmid genes was demonstrated in E. coli.     

Effects of heavy central metal on the ground and excited states of chlorophyll

Chlorophylls, owing to their adjustable π-electron system and intense, well-separated electronic transitions, can serve as convenient intrinsic spectroscopic probes of ligand–metal center interactions. They are also interesting for their photosensitizing properties. In order to examine the heavy-atom effects on the chlorophyll triplet state, a key intermediate in chlorophyll–photosensitized reactions, the synthesis of a novel Pt(II)-substituted chlorophyll a was carried out, and the effects of the substitution on steady-state and transient photophysical properties of chlorophyll were studied by absorption and fluorescence spectroscopies, and by laser flash photolysis. The presence of highly electronegative platinum as the central ion increases the energies of the chlorophyll main absorption transitions. As laser flash photolysis experiments show, in air-equilibrated solutions, chlorophyll triplets are efficiently quenched by molecular oxygen. Interestingly, this quenching by oxygen is more effective with metal-containing pigments, in spite of the increased spin–orbit coupling, introduced with the central metals. This points to occurrence of nonspecific interactions of molecular oxygen with metallochlorophylls. The differences in the effects exerted on the pigment triplet by the central metal become distinct after the removal of oxygen. The lifetime of a Pt-chlorophyll triplet remains very short, in the range of only a few microseconds, unlike in the free-base and Mg- and Zn-substituted chlorophylls. Such drastic shortening of the triplet lifetime can be attributed to a large heavy-atom effect, implying that strong interactions must occur between the central Pt(II) ion and the chlorophyll macrocycle, which lead to a more efficient spin–orbit coupling in Pt-chlorophyll than in Pt-porphyrins.Electronic Supplementary Material Supplementary material is available for this article at .