A large multigene family codes for the polypeptides of the crystalline trichocyst matrix in Paramecium.

The secretory granules (trichocysts) of Paramecium are characterized by a highly constrained shape that reflects the crystalline organization of their protein contents. Yet the crystalline trichocyst content is composed not of a single protein but of a family of related polypeptides that derive from a family of precursors by protein processing. In this paper we show that a multigene family, of unusually large size for a unicellular organism, codes for these proteins. The family is organized in subfamilies; each subfamily codes for proteins with different primary structures, but within the subfamilies several genes code for nearly identical proteins. For one subfamily, we have obtained direct evidence that the different members are coexpressed. The three subfamilies we have characterized are located on different macronuclear chromosomes. Typical 23-29 nucleotide Paramecium introns are found in one of the regions studied and the intron sequences are more variable than the surrounding coding sequences, providing gene-specific markers. We suggest that this multigene family may have evolved to assure a microheterogeneity of structural proteins necessary for morphogenesis of a complex secretory granule core with a constrained shape and dynamic properties: genetic analysis has shown that correct assembly of the crystalline core is necessary for trichocyst function.     

Approaches to breeding for salinity tolerance - a case study on Porteresia coarctata

Cereals are the world's major source of food for human nutrition. Among these, rice (Oryza sativa) is the most prominent and represents the staple diet for more than two-fifths (2.4 billion) of the world's population, making it the most important food crop of the developing world (Anon., 2000a). Rice production in vast stretches of coastal areas is hampered due to high soil salinity. This is because rice is a glycophyte and it does not grow well under saline conditions. In order to increase rice production in these areas there is a need to develop rice varieties suited to saline environments. Research has shown that Porteresia coarctata, a highly salt tolerant wild relative of rice growing in estuarine soils, is an important material for transferring salt tolerant characteristics to rice. It is quite possible that Porteresia may be used as a parent for evolving better and truly salt resistant varieties. The inadequate results and the difficulties associated with conventional breeding techniques necessitate the use of the tools of crop biotechnology in unravelling some of the characteristics of Porteresia that have been highlighted in this report. In view of the limited resources available for increasing salinity tolerance to the breeders to wild rice germplasm, Porteresia is undoubtedly one of the key source species for elevating salinity tolerance in cultivated rice.     

Albumin extinction followed by de novo methylation of its gene in somatic hybrids of a rat hepatoma

We have previously identified an Msp I site at the 5′ end of the rat albumin gene whose undermethylation is necessary but not sufficient for stable albumin expression in rat hepatoma cells [1]. We have also shown that the extinction of albumin expression in somatic hybrids is not the result of methylation at this site, since for two different crosses, rapid extinction was found to occur in the absence of any de novo methylation of the previously active gene[2]. In the present study, we examine albumin expression and albumin gene methylation for independent hybrid clones isolated from crosses between albumin expressing rat hepatoma cells and cells of two different non-expressing lines. The cells from hybrid clones of both crosses are characterized by stable extinction of albumin expression. Moreover, we find that de novo methylation of the “extinguished” albumin gene can occur in somatic hybrids, but only some weeks after the gene has ceased to be expressed.     

Photosensory retinal pigments in Halobacterium halobium

In Halobacterium halobium, nicotine is known to block the synthesis of retinal. Cells grown in the presence of nicotine do not show any photophobic response. Addition of retinal₁ or retinal₂ restored the photophobic responses to light-increase in the UV and to light-decrease in the green-yellow part of the spectrum. The action spectra of the two retinal₂-photosystems were red-shifted by 15–20 nm, compared with the corresponding retinal₁ systems. We conclude that each of the two photosystems, PS 370 and PS 565, has its own photosensory pigment with retinal as the chromophoric group.     

The composition and the structure of bacterioferritin of Escherichia coli.

Bacterioferritin isolated from Escherichia coli is of two kinds: a protein containing a polynuclear iron compound, the bacterioferritin proper and a protein free of the polynuclear iron compound, the apo-bacterioferritin. Bacterioferritin of both kinds is characterized by absorption maxima at 417,530 and 560 nm, contributed by protohaem IX. Single crystals of bacterioferritin of the space group I432 suggest that the molecule is made up of 24 identical subunits related by a cubic point symmetry. The molecular weight of the protein subunit, as determined by sodium dodecyl sulphate/polyacrylamide-gel electrophoresis, is 15000. In the electron microscope the bacterioferritin molecule appears to be a sphere of 9.5 nm (95 A) diameter composed of a negatively staining outer shell and an inner electron-dense core of 6 nm (60 A) diameter.     

On the dynamics of exploited populations ofTisbe holothuriae (Copepoda,Harpacticoidae)

A total of 90, weekly exploited populations of the harpacticoid copepodTisbe holothuriae Humes were exposed to 148, 222, 333, 500, 750 or 1125µg Cd⁺⁺ l^–1, combined with exploitation rates of 10, 30, 50, 70 or 90% under conditions of surplus food supply at 22° C and 30 S. All populations exposed to concentrations down to 500µg Cd⁺⁺ l^–1 and 3 populations (out of 15) exposed to 333µg l^–1 became extinct within the experimental period of 30 weeks. Survival time significantly depended on concentration. A recovery phase from an initially high mortality preceded eventual population extinction after adding 500µg Cd⁺⁺ l^–1. In the initial phase, higher nauplii mortality prevailed. During these experiments on acute intoxication, no relationship could be established between survival and exploitation rate. However, experiments on the effects of stepwise increases in Cd concentration (results not yet published) produced evidence of such a relationship. In spite of increased mortality, no significant numbers of dead copepods were detected in weekly samples because of their rapid decomposition and cannibalism, which depends on the amount of food available. Sampling regimes of 5 times per week yielded significant numbers of dead individuals.     

Metabolism of Guanine and Guanine Nucleotides in Primary Rat Neuronal Cultures

The metabolic fate of guanine and of guanine ribonucleotides (GuRNs) in cultured rat neurons was studied using labeled guanine. 8-Aminoguanosine (8-AGuo), an inhibitor of purine nucleoside phosphorylase, was used to clarify the pathways of GMP degradation, and mycophenolic acid, an inhibitor of IMP dehydrogenase, was used to assess the flux from IMP to GMP and, indirectly, the activity of the guanine nucleotide cycle (GMP----IMP----XMP----GMP). The main metabolic fate of guanine in the neurons was deamination to xanthine, but significant incorporation of guanine into GuRNs, at a rate of approximately 8.5-13.1% of that of the deamination, was also demonstrated. The turnover rate of GuRNs was fast (loss of 80% of the radioactivity of the prelabeled pool in 22 h), reflecting synthesis of nucleic acids (32.8% of the loss in radioactivity) and degradation to xanthine, guanine, hypoxanthine, guanosine, and inosine (49.3, 4.3, 4.1, 1.1, and 0.5% of the loss, respectively). Of the radioactivity in GuRNs, 7.9% was shifted to adenine nucleotides. The accumulation of label in xanthine indicates (in the absence of xanthine oxidase) that the main degradative pathway from GMP is that to xanthine through guanosine and guanine. The use of 8-AGuo confirmed this pathway but indicated the operation of an additional, relatively slower degradative pathway, that from GMP through IMP to inosine and hypoxanthine. Hypoxanthine was incorporated mainly into adenine nucleotide (91.5%), but a significant proportion (6%) was found in GuRNs.(ABSTRACT TRUNCATED AT 250 WORDS)     

A murine CD4-, CD8- T cell receptor-gamma delta T lymphocyte clone specific for herpes simplex virus glycoprotein I.

The role of TCR-gamma delta T lymphocytes in immune responses is currently not well understood. TCR-gamma delta cells have a limited repertoire suggesting that TCR-gamma delta T a limited number of evolutionarily conserved Ag such as nonpolymorphic MHC and heat shock proteins. TCR-gamma delta T lymphocytes appear in enhanced numbers in skin lesions produced by Mycobacterium leprae and in the synovial fluid of joints affected by rheumatoid arthritis, raising the possibility that this subset of T lymphocytes may play a role in control of infectious processes and in autoimmune diseases. We report the identification of a TCR-gamma delta T cell clone isolated from a HSV-infected mouse that recognizes glycoprotein I of HSV type 1. Clone recognition of glycoprotein I does not appear to require the expression of MHC class I or class II gene products. These data suggest that TCR-gamma delta lymphocytes may play an important role in the immune response to viral infections.