Volume 18, Issue 1
March 1993, pages 1-160
pp 1-11 March 1993
Search for a promoter element by RNA polymerase from the extremely large DNA base sequence is thought to be the slowest and rate-determining for the regulation of transcription process. Few direct experiments we described here which have tried to follow the mechanistic implications of this promoter search. However, once the promoter is located, transcription complex, constituting mainly the RNA polymerase molecule and few transcription factors has to unidirectionally clear the promoter and elongate the RNA chain through a series of steps which altogether define the initiation of transcription process. Thus, it appears that the promoter sequence acts as a trap for RNA polymerase associated with a large binding constant, although to clear the promoter and to elongate the transcript such energy barrier has to be overcome. Topological state of the DNA, particularly in the neighbourhood of the promoter plays an important role in the energetics of the whole process
pp 13-25 March 1993
Mechanism of control of transcription initiation have expanded far beyond the classical operon concept. Control elements are multipartite and well separated from each other. Thetrans-factors bound to these sites make contacts with RNA polymerase: promoter complexes by DNA bending or looping to influence the initiation event. Activators and repressors are like two faces of the same coin and their function depends on the site of action, mode of interaction with DNA and also the nutritional status of the cell.
pp 27-36 March 1993
The regulation of eukaryotic gene transcription poses major challenges in terms of the innumerable protein factors required to ensure tissue or cell-type specificity. While this specificity is sought to be explained by the interaction of cis-acting DNA elements and thetrans-acting protein factor(s), considerable amount of degeneracy has been observed in this interaction. Immunoglobulin heavy chain gene expression in B cells and liver-specific gene expression are discussed as examples of this complexity in this article. Heterodimerization and post-translational modification of transcription factors and the organization of composite promoter elements are strategies by which diverse sets of genes can be regulated in a specific manner using a finite number of protein factors
pp 37-45 March 1993
Earlier work from this laboratory had identified, mapped and characterised an intragenic suppressor(fitA24) as well as an extragenic suppressor(fitB) for the temperature-sensitive transcription defective mutationfitA76 inEscherichia coli In this communication we report the results of experiments on RNA synthesis and decay of pulse labelled RNA in strains harbouringfit A76,fitB, fitA24, fitA76-fitA24, fitA76-fitB mutation(s) as well as in the isogenicfitA+ fitB+ strain. Taken together with earlier results, this indicates that thefitA andfitB gene products could be involved in the expression of some classes of genes including genes coding for ribosomal proteins. The implications of these results for thein vivo control of transcription inEscherichia coli are discussed.
pp 47-57 March 1993
Quiescent cultures of rat embryo fibroblasts synthesize and secrete several proteins in response to mitogenic stimulation. Two of these proteins have been characterized in this study and the effect of oncogenic transformation on these proteins was monitored. A serum induced 48,000 protein was shown to be related to plasminogen activator inhibitor while another serum-induced protein ofMr 45,000 was found to be an inhibitor of DNA synthesis. Transformation of rat embryo fibroblasts with oncogenesmyc andras resulted in drastic reduction in the level of these proteins. The reduced levels of protease inhibitor may be responsible for the loss of anchorage dependence of the transformed cells. The DNA synthesis inhibitor protein may act as a negative growth regulator and reduced levels of this protein inmyc-ras transformed cells may accelerate the proliferation of these cells.
pp 59-72 March 1993
In adult rats, removal of one ovary leads to an acute albeit transient rise in serum follicle stimulating hormone and an increase in the weight of the remaining ovary. In an attempt to correlate the high titre of endogenous follicle stimulating hormone with the changes taking place at the macromolecular level, the phenomenon of compensatory ovarian hypertrophy was studied for one cycle after hemiovariectomy at metoestrus in the adult, cycling female rats derived from the Holtzman strain. The significant finding with respect to hormonal changes was an acute follicle stimulating hormone surge commencing 6h post-unilateral ovariectomy, reaching a maximum at 12 h and declining thereafter, hitherto not reported in the Holtzman strain. Serum luteinizing hormone, prolactin, oestradiol-17β and testosterone remained unaltered while progesterone showed a decline at 6 h after surgery. There was an increase in the number of healthy class III (> 350 µm) follicles with a concomitant drop in atretic class III follicles 24 h post-unilateral ovariectomy. Analysis for DNA, RNA and protein content showed that all three constituents registered a continuous rise in the hypertrophying ovary up to 120h after surgery. When expressed as ¼g/mg ovarian weight, the increase in DNA reached a maximum at 24 h and declined thereafter. The kinetics of DNA synthesis was followed by pulse labelling with [3H] thymidine at 18, 24, 36 and 48 h after unilateral ovariectomy. Maximum incorporation occurred at 36 h. Autoradiographic studies showed that the granulosa cells of healthy follicles preferentially incorporated the label. In an extension of this study, it was found that labelling index registered a significant increase following ovariectomy, the maximum being reached at 24 h especially in classIII follicles. The results clearly point out the crucial role of hyperplasia in the response of the contralateral ovary to the surgery and implicate the rise in follicle stimulating hormone as the primary signal for initiation of such a response. This raises the question whether in compensatory ovarian hypertrophy follicle stimulating hormone has a mitogenic role
pp 73-82 March 1993
Microsomal membrane vesicles isolated from goat spermatozoa contain Ca2+-ATPase, and exhibit Ca2+ transport activities that do not require exogenous Mg2+ .The enzyme activity is inhibited by calcium-channel inhibitors,e.g. verapamil and diltiazem, like the well known Ca2+ , Mg2+-ATPase. The uptake of calcium is ATP (energy)-dependent and the accumulated Ca2+ can be completely released by the Ca2+ ionophore A23187, suggesting that a significant fraction of the vesicles are oriented inside out
pp 83-91 March 1993
In isolated scale melanophores ofLabeo rohita the melanosome aggregating effect of K+ was inhibited in Ca2+ deprived medium. Moreover, the Ca2+-antagonists, verapamil and lanthanum inhibited the action of K+ in concentration dependent manner. The elevation of extracellular Ca2+ could compromise the verapamil induced inhibition in a concentration dependent manner. The cation Ca2+ appeared to be required only for K+ -induced aggregation and not melanosome aggregationper se, as in this fish adrenaline and melanin concentrating hormone effectively caused aggregation of melanosomes in Ca2+ free medium
pp 93-101 March 1993
Various plant parts ofIndigofera tinctoria L. were collected separately at different growth stages and analysed for their rotenoid content. The total rotenoid content decreased with age; among the plant parts, maximum content was in leaves and minimum in stem. The identity of different rotenoids was confirmed by melting point, mixed melting point, UV and infrared spectral studies, and gas-liquid chromatography. Six rotenoids (deguelin, dehydrodeguelin, rotenol, rotenone, tephrosin and sumatrol) were isolated, identified and quantified invivo.
The static cultures ofIndigofera tinctoria were established from seeds on RT medium, and maintained for a period of six months by frequent subculturings. Only four rotenoids were present in callus cultures; sumatrol and tephrosin were absent. The maximum content was found in eight week old tissue after fresh subculturings and minimum at 2 weeks.
The toxicological studies ofin vivo andin vitro extract against the pulse beetle(Callosobruchus chinensis) and mosquito(Anopheles stephensi) larvae, showed that rotenoids were more effective against mosquito larvae thanCallosobruchus chinensis. Extracts from callus was more effective against both the test animals than that from plant parts.
pp 103-110 March 1993
Single 2h administration of diazepam (benzodiazepine) in 3.5% ethanol solution was found to evoke advance and delay phase shifts in the locomotor activity rhythm in the field mouseMus booduga. Through such pulsed administration of diazepam at various phases of circadian rhythm a phase response curve could be constructed. Phase advance occurred during early subjective day (CT 2) and phase delays were observed in the remaining phases. The shape of the diazepam phase response curve is similar to the general shape of the phase response curves generated by intraperitoneal injections of other benzodiazepines in hamsters. The phase shifting action of diazepam may be explained by its agonistic action on the neurotransmitter gamma-aminobutyric acid.
pp 111-119 March 1993
Common myna(Acridotherus tristis) and jungle myna(Acridotherus fuscus) forage in pure and mixed flocks of various sizes in fallow lands. These flocks were often found associated with drongos that forage individually on the insects herded out by the movements of the flocking myna. We report here the benefits and costs of such association to drongos and mynas. Drongos had a tendency to associate with larger (> 21) than smaller (<20) flocks irrespective of the species composition of the flocks. Drongos associated with larger flocks showed increased foraging trips and harvested more insects in a given time than those that were either isolated or were associated with small flocks. The food range of drongos and mynas differed significantly indicating that they do not compete with each other. Thus our results indicate that drongos are benefitted by this association; however this association neither benefits nor costs to the mynas. The association between the drongos and mynas therefore appears to be commensalistic.
pp 121-139 March 1993
Amphibian community structure in five tropical sites was studied using dominance, diversity, evenness indices, niche breadth and overlapping scores and association analysis. Ten species of amphibians with average density/ha varying from 8 to 49 in different sites were collected.Rana limnocharis andBufo melanostictus were respectively the dominant amphibia in paddy fields and other sites. Niche breadth scores indicatedRana limnocharis, Bufo melanostictus andRana cyanophlyctis as habitat generalists indicating wide tolerance to environmental gradients. Five frog speciesi.e. Rana tigerina, Microhyla ornata, Ramanella variegata, Uperedon systoma andPolypedates maculatus were considered habitat specialists indicating narrow tolerance to environmental gradients. Niche breadth scores were found to be a function of the cumulative relative abundance value of different species. The niches ofRana limnocharis andRana cyanophlyctis, Bufo melanostictus andBufo stomaticus showed maximum overlapping.Rana tigerina showed maximum niche overlapping withRana variegata in paddy fields and withMicrohyla ornata when all sites were taken together. The coefficient of community index was maximum between the paddy fields and minimum between the paddy fields and forest site.Rana tigerina occurred very sparsely and analysis of data indicates that its population are threatened and require conservation measure.
pp 141-148 March 1993
Zooplankton sampling was carried out during the first six Indian Scientific Expeditions to Antarctica (1981—1987) to estimate krill abundance in the Indian sector of the southern ocean (between 35° to 70° S and 10° to 52° E). This study aims to understand the distribution of biomass of zooplankton, especially the krill, using the data collected by net sampling techniques. Total zooplankton biomass for all the sampling stations ranged from 9 to 684 ml/1000m3 (x: 143.34±138.61 SD; n=150). Biomass data grouped by 5° latitude interval shows the presence of higher biomass (x: 191 ml/1000 m3;n = 31) in the Antarctic divergence region (between 60° to 65° S). EuphausiidEuphausia superba DANA formed a considerable component of biomass and together with eggs and larvae represented over 60% (n = 39) of mean total zooplankton-biomass in the coastal ice region. The values for population density and biomass of adult-size krill varied between 0 to 4320 individuals and 6 to 305 ml/1000 m3, respectively.
The highest values were recorded between 62° to 69° S and between 16° to 30° E. A high density of krill larvae was encountered in the shelf region during January 1987 which was related to chlorophyll concentration. However, the values obtained during six consecutive summers showed that values of adult krill biomass at given location was highly variable and, hence, not comparable on inter-annual basis, during the sampling years.
pp 149-153 March 1993
The burrow density of sympatric murids in relation to various abiotic factorsviz. maximum and minimum atmospheric temperatures, relative humidity, soil temperature and soil moisture was studied in the agro-ecosystem of village Kakrod-Jind (Haryana) Analysis of monthly recorded data on burrow density revealed a biomodal patterni. e. a peak each during the months of September and March · Of these abiotic factors, soil moisture revealed significant positive correlation with the burrow density whereas relative humidity exhibited invariably the least interaction · However, path co-efficient analysis depicted the direct effects of soil temperature and soil moisture and indirect effect of maximum and minimum atmospheric temperature through soil temperature on the burrow density. The use of path co-efficient analysis in such studies has been suggested.
pp 155-160 March 1993
Numerous prokaryotes, belonging to physiologically and taxonomically different groups, are able to produce hydrogen. Some photosynthetic bacteria have the property of light-dependent production of hydrogen from organic substrates. We isolated several photosynthetic purple and green bacteria from enrichment cultures made from the water of a waste-water pond of a cool-drink refilling station. After testing them for their ability to use various organic compounds as carbon source, and sulphide, thiosulphate and organic compounds as electron donor, we selected the fastest-growing isolate, aRhodopseudomonas, for a study of its ability to produce molecular hydrogen in presence of light. Immobilized cells of this isolate produced significant amounts of hydrogen from both sewage and waste water
Volume 44 | Issue 5
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