Volume 24, Issue 4
December 1999, pages 409-559
pp 409-411 December 1999 Clipboard
pp 411-412 December 1999 Clipboard
pp 413-415 December 1999 Commentary
pp 417-420 December 1999 Perspectives
Is Science chauvinistic? It is not, but scientists often are. How does chauvinism in Science manifest itself? Could it be that we are genetically programmed to reject those we see as “foreign”?
pp 421-426 December 1999 Articles
Structural rearrangements of chromosomes have played a decisive role in the karyotypic evolution of species. It is also known that inversions, translocations, fusions, fissions, heterochromatin variations and other chromosomal changes occur as transient events in natural populations. Herein we report the occurrence of a rare event of centric fission of a metacentric chromosome in a laboratory population ofDrosophila, called Cytorace 1. This centric fission has been fixed in a sub-population of Cytorace 1, resulting in a new chromosomal lineage called Fissioncytorace-1.
pp 427-431 December 1999 Articles
Drosophila ananassae, a cosmopolitan and domestic species, belongs to theananassae subgroup of themelanogaster species group. Female remating was observed in ten mass culture stocks of this species, which were initiated from flies collected from different geographic localities. The frequency of female remating ranges from 24% to 56% in different strains. Strains show significant variation in remating latency (days). Significant variation has also been found in all the stocks for duration of copulation between first and second matings. The duration of copulation is shorter in second mating as compared to first mating inD. ananassae.
pp 433-440 December 1999 Articles
Genetic relationships were evaluated among nine cultivars ofBrassica campestris by employing random amplification of polymorphic DNA (RAPD) and amplified fragment length polymorphism (AFLP) markers. RAPDs generated a total of 125 bands using 13 decamer primers (an average of 9.6 bands per assay) of which nearly 80% were polymorphic. The per cent polymorphism ranged from 60–100%. AFLP, on the other hand generated a total of 319 markers, an average of 64 bands per assay. Of these, 213 were polymorphic in nature (66.8%). AFLP methodology detected polymorphism more efficiently than RAPD approach due to a greater number of loci assayed per reaction. Cultivar-specific bands were identified, for some cultivars using RAPD, and for most cultivars with AFLP. Genetic similarity matrix, based on Jaccard’s index detected coefficients ranging from 0.42 to 0.73 for RAPD, and from 0.48 to 0.925 for AFLPs indicating a wide genetic base. Cluster analyses using data generated by both RAPD and AFLP markers, clearly separated the yellow seeded, self-compatible cultivars from the brown seeded, self-incompatible cultivars although AFLP markers were able to group the cultivars more accurately. The higher genetic variation detected by AFLP in comparison to RAPD was also reflected in the topography of the phenetic dendrograms obtained. These results have been discussed in light of other studies and the relative efficiency of the marker systems for germplasm evaluation.
pp 441-444 December 1999 Articles
Accumulation of immunoglobulin Ig RNA (from several loci viz., CH, Cα, Jk-Ck and Sμ during Igμ isotype switching) in B cells and T cell receptor (TCR) RNAs (α, β andγ) in T cells of unusual sizes emanating from germline and rearranged genes were reported to accumulate in human and mouse (and murine too). The precise mechanism and function of these sterile RNA species are yet to be delineated. Similar accumulation of RNA species of unusual sizes were identified with DNA-RNA hybridization and isolation of cDNA employing with DNA and antibody probes in mouse hybridoma, murine tumour, non-human primate marmoset tumour and human leukemic cells.
pp 445-452 December 1999 Articles
Helicoverpa armigera is a major pest of many tropical crop plants. Soybean trypsin inhibitor (SBTI) was highly effective against the proteolytic activity of gut extract of the insect. SBTI was also inhibitory to insect growth when present in artificial diet. The gene coding for SBTI was cloned from soybean (Glycine max, CVBirsa) and transferred to tobacco plants for constitutive expression. Young larvae ofH. armigera, fed on the leaves of the transgenic tobacco plants expressing high level of SBTI, however, maintained normal growth and development. The results suggest that in certain cases the trypsin inhibitor gene(s) may not be suitable candidates for developing insect resistant transgenic plants.
pp 453-459 December 1999 Articles
The ω subunit ofEscherichia coli RNA polymerase is a 91 amino acid polypeptide which co-purifies with the enzyme and is thought to help in maturing the rest of the enzyme to its full functionality. Purified ω when added externally was found to inhibit general transcriptional activity of ω-less RNA polymerase as well as promoter-specific single-round transcriptional activity at all the promoters tested. In this study we have tried to analyse the observed inhibition of transcription using gel retardation assays and KMnO4 foot-printing. Further, through protein foot-printing we have attempted to identify alterations in the interaction of the ω-less core enzyme with the σ70 subunit.
Our results suggest that the ω-less holoenzyme has lesser affinity towards the DNA template and external addition of ω destabilizes the open complex for both the wild-type and ω-less enzyme. The ω-less core enzyme interacts with the σ70 subunit to expose the — 35 recognition domain (domain 4.2) unlike that observed in the wild-type interaction. Thus the absence of the ω subunit leads to the formation of an enzyme which has altered DNA binding and σ70binding properties. Circular dichroic measurements also indicate a major conformational alteration of both holo and core RNA polymerase in the presence and absence of the ω subunit.
pp 461-470 December 1999 Articles
Melanocarpus albomyces, a thermophilic fungus isolated from compost by enrichment culture in a liquid medium containing sugarcane bagasse, produced cellulase-free xylanase in culture medium. The fungus was unusual in that xylanase activity was inducible not only by hemicellulosic material but also by the monomeric pentosan unit of xylan but not by glucose. Concentration of bagasse-grown culture filtrate protein followed by size-exclusion and anion-exchange chromatography separated four xylanase activities. Under identical conditions of protein purification, xylanase I was absent in the xylose-grown culture filtrate. Two xylanase activities, a minor xylanase IA and a major xylanase IIIA, were purified to apparent homogeneity from bagasse-grown cultures. Both xylanases were specific forβ-1,4 xylose-rich polymer, optimally active, respectively, at pH 6.6 and 5.6, and at 65°C. The xylanases were stable between pH 5 to 10 at 50°C for 24 h. Xylanases released xylobiose, xylotriose and higher oligomers from xylans from different sources. Xylanase IA had a Mr of 38 kDa and contained 7% carbohydrate whereas xylanase IIIA had a Mr of 24 kDa and no detectable carbohydrate. The Km for larchwood xylan (mg ml−1) and Vmax (μmol xylose min−1 mg−1 protein) of xylanase IA were 0.33 and 311, and of xylanase IIIA 1.69 and 500, respectively. Xylanases IA, II and IIIA showed no synergism in the hydrolysis of larchwood glucuronoxylan or oat spelt and sugarcane bagasse arabinoxylans. They had different reactivity on untreated and delignified bagasse. The xylanases were more reactive than cellulase on delignified bagasse. Simultaneous treatment of delignified bagasse by xylanase and cellulase released more sugar than individual enzyme treatments. By contrast, the primary cell walls of a plant, particularly from the region of elongation, were more susceptible to the action of cellulase than xylanase. The effects of xylanase and cellulase on plant cell walls were consistent with the view that hemicellulose surrounds cellulose in plant cell walls.
pp 471-476 December 1999 Articles
This study demonstrated that a marine Indian horseshoe crab,Carcinoscorpious rotundacauda showed higher self defence in an experimental infection upon the induction of its circulatory lectin, carcinoscorpin. It resisted an infection with 107 liveEscherichia coli per crab when the circulatory carcinoscorpin was 8–16-fold higher after administering 2-ketodeoxyoctonate (Kdo) into the live crab. The naive control with its natural level of circulatory lectin could tolerate a maximum infective dose of 106 liveE. coli per crab. Bacterial killing and phagocytic uptake in association with the isolated crab amoebocytes in anex vivo system was considerably higher for the lectin opsonizedE. coli compared to unopsonized samples. Carcinoscorpin is thus functionally an opsonin in the defence of the primitive marine arthropod,C. rotundacauda, like vertebrate antibody, a humoral factor involved in the defence of the host. The natural capacity for defending an infection with 106 liveE. coli per crab suggested that the crabs in the natural habitat hardly face such an infection and is possibly one of the reasons for its survival over millions of years as a living fossil.
pp 477-481 December 1999 Articles
Genetic alterations in the p53 tumour suppressor gene of human chromosome 17 have been frequently found to be associated with various tumours. Glial tumours arise from the supporting cells of the brain. They have a poor outcome and often recur. The present study was undertaken to compare the loss of heterozygosity (LOH) of p53 gene in pairs of primary and recurrent gliomas and to try and correlate it to the degree of malignancy and recurrence interval. LOH of p53 was taken as an indicator of the inactivation of p53 due to genetic changes. Ten patients with recurrent gliomas were studied. Three patients had LOH at primary surgery and two of these had LOH at recurrent surgery. One patient had LOH of p53 only at recurrent surgery but not at primary surgery. No indicative correlation was found between p53 heterozygosity status on one hand and grade of malignancy (primary and recurrent) and recurrence interval on the other.
pp 483-490 December 1999 Articles
Nitric oxide synthase (NOS) catalyzes the formation of nitric oxide (NO) from L-arginine. In this study, the cellular localization of neuronal NOS (nNOS) activity in the human retina since fetal development was examined by immunohistochemistry. No detectable staining in the fetal retina was present at 14 weeks of gestation (wg), the earliest age group examined. A centro-peripheral gradient of development of nNOS immunoreactivity was evident at 16–17 wg, with the midperipheral retina showing nNOS immunoreactivity in most of the cell types and the inner plexiform layer while the peripheral part demonstrated moderate immunoreactivity only in the ganglion cell layer and photoreceptor precursors. A transient increase in nNOS immunoreactivity in the ganglion cells and Müller cell endfeet between 18–19 and 24–25 wg was observed at the time when programmed cell death in the ganglion cell layer, loss of optic nerve fibres as well as increase in glutamate immunoreactivity and parvalbumin (a calcium binding protein) immunoreactivity in the ganglion cells was reported. These observations indicate that programmed cell death of ganglion cells in the retina may be linked to glutamate toxicity and NO activity, as also suggested by others in the retina and cerebral cortex.
The presence of nNOS immunoreactivity in the photoreceptors from 16–17 weeks of fetal life to adulthood indicates other functions, besides their involvement in photoreceptor function of transduction and information processing.
pp 491-498 December 1999 Articles
The stable carbon and oxygen isotope ratios in cellulose of C3 and C4 plants growing on the surface of a montane peat bog in the Nilgiri hills, southern India, were measured. The mean monthly δ13C values in cellulose of both C3 and C4 plants are found to be significantly related to rainfall, while the δ18O values are sensitive to changes in maximum temperature and relative humidity of the region. Further, higher δ18O values were observed in C4 plants compared to C3 plants, suggesting that C4 plants are probably less sensitive to relative humidity as compared to C3 plants and are able to photosynthesize even during drier conditions. The plant isotope-climate correlations thus established can be used for reconstructing the past temperature and rainfall conditions of the tropics from the isotopic ratios of peat deposits, derived from a mixture of C3 and C4 plants in the region.
pp 499-514 December 1999 Review
Plants have evolved highly sensitive sensory photoreceptor systems to regulate various aspects of their growth and development. Many responses such as seed germination, flowering and dormancy are controlled by red and far-red regions of the solar spectrum through the phytochrome family of photoreceptors. However, several other responses such as stem growth inhibition, phototropism and opening of stomata are controlled by blue and/or ultraviolet light absorbing photoreceptors called cryptochromes and phototropin.
Despite their central role in plant biology, the mode of action of these photoreceptors has been shrouded in mystery. Even the biochemical isolation of a photoreceptor, as in the case of phytochrome was accomplished decades ago, did not help in elucidating the mechanism of action. Nevertheless, due to advances in recombinant DNA technology, generation of extensive databanks and the capability to predict function by base sequence analysis, a breakthrough has now come about. It is clear that certain phytochromes, at least in the cyanobacteria and algae which represent the simplest plants, are hybrid photoreceptor-cum-kinases. These novel kinases utilize captured photons rather than conventional ligands to trigger conformational change and in consequence enzyme activity. The kinases apparently, then, cause phosphorylation of many other types of target molecules, leading eventually to various developmental changes. There is suggestive evidence that in higher plants, too, at least some phytochromes may operate as kinases.
As compared to work on phytochromes, the blue light photoreceptors have begun to be studied only recently. However, the exciting discovery has been made of at least one photoactive kinase that is critically required for phototropism.
This article summarizes the above discoveries from the perspective of general biology.
pp 515-528 December 1999 Review
Temporal and spatial gene expression and inductive interactions control the establishment of the body plan during embryogenesis in invertebrates and vertebrates. The best-studied vertebrate model system is the amphibian embryo. Seventy-five years after the famous organizer experiment of Hans Spemann and Hilde Mangold in 1924 our knowledge of the molecular mechanisms of the multi-step formation of embryonic axis has substantially improved. Although in the 30s and 40s the interest of many laboratories was focussed on neural induction (determination of the central nervous system), only crude factors from so-called heterogeneous inducers (liver, bone marrow, etc.,) could be isolated by the traditional biochemical techniques available at this time. An important breakthrough was the characterization and purification of a mesoderm inducing factor, the so-called vegetalizing factor (homologous to Activin) in highly purified from chicken embryos. Much later after the introduction of molecular techniques Vgl and Activin (both belonging to the TGF-β family) and FGFs could be identified as important factors for mesoderm formation. It was in the 90s that secreted neuralizing factors (chordin, noggin, follistatin and cerberus) could be detected, which are expressed at the dorsal side of the early embryo including the Spemann organizer. In contrast to the classical view, these proteins act as antagonists to factors like BMP-4 localized on the ventral side. Of special interest was the fact that inDrosophila sog, homologous to chordin, determines the ventral side, whiledpp, homologous toBMP-4, participates in the formation of the dorsal side. These data of evolutionary conserved genes in both invertebrates and vertebrates support the view that they are descendents of common ancestors, the urbilateralia, living around 300 million years ago. The expression of those genes coding for secreted proteins is closely related to inductive interactions between cells and germ layers. Recently it was shown that planar signals are not sufficient to generate a specific anterior/posterior pattern during the primary steps of neural induction, i.e., formation of the central nervous system in amphibians.
pp 529-559 December 1999 Review
This review is focused on the physiological and evolutionary strategies of the processes occurring during the entry of microbial cells into stationary phase and the subsequent period of stasis. The molecular mechanisms adapting microorganisms from exponential growth to a static state involve activation and complex regulation of the stationary factor Sigma-S, which directs RNA polymerase to the specific promoters. As a result the static cells acquire general resistance (simultaneous tolerances) to different environmental stresses. In parallel with the physiological adaptation to stasis, diverse genetical processes are aimed towards resuming the growth of the static cells. Different types of mutagenesis occur: (i) in cells entering stasis and (ii) in static cells (adaptive mutagenesis). Cessation of growth induces the transient hypermutator state resulting in the accumulation of random mutations in the subpopulation of the static cells. If by chance, one or a few of such mutations lead to resumption of division, the growing cell will return to a normal mechanism of spontaneous mutagenesis.
Another mechanism for generating genetical variability in stressed cells involves transposons and conjugative plasmids. Stresses can stimulate the excision of some transposons, which, in turn, can generate chromosomal mutations and activate intracellular mechanisms of mutagenesis. Under stress some conjugative plasmids activate genes encoding antirestriction proteins that repress restriction-modification systems of the recipient cells. Moreover, under stress special cellular mechanisms decrease (alleviate) the activity of restriction-modification systems which, in turn, enhance the probability of gene transfer into the stressed cells.
Under stress, the efficiency of inter-species genetical barriers also decreases. This, stimulates inter-species gene transfer and may lead to a burst of incipient speciation in the population of non-growing cells. After resumption of growth the genetical barriers leading to isolation will be restored.
In general, the cessation of growth “switches on”, and resumption of growth “switches off”, a set of special processes that are responsible for generating bursts of genetical variability in populations of microorganisms.
Volume 44 | Issue 5
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