Showing papers by "University of Sussex published in 1976"

Mutagen testing using TRP+ reversion in Escherichia coli.

Abstract: Escherichia coli strain WP2 and its repair-deficient derivatives are suitable strains for mutagen screening. In these strains, agents which cause base substitution mutations can be shown to increase the frequency of Trp+ revertants. In addition, agents causing many types of DNA damage can be detected through increased killing of the repair deficient derivatives. Four ways of performing tests are described: (a) Spot tests in which a small amount of the agent under test is placed directly on a selective agar plate. Trp+ revertants are counted and increased sensitivity of repair-deficient strains determined from the size of the zone of inhibition of cell growth. (b) Treat and plate tests, where a strain is treated with the agent under test and subsequently plated to determine survival or frequency of Trp+ revertants. (c) A simplified fluctuation test which shows exceptional sensitivity in measuring mutation with low levels of mutagens. (d) Use of a liver microsomal fraction in conjunction with treat and plate tests to detect metabolically activated mutagens. The merits and defects of these systems are discussed. Common pitfalls in evaluating tests and procedures for avoiding them are described.

Why be an hermaphrodite

Abstract: MANY animals and most higher plants are hermaphrodites. The basic argument of this paper is that the sex habit of a species is determined by selection acting on the number of offspring produced by individuals of different types. The argument differs radically from most earlier explanations of the evolution of hermaphroditism (reviewed by Ghiselin)1,2, although it is formally similar to a recent explanation3 of sequential hermaphroditism, in which individuals function first as one sex and then the other.

Receptor-binding region of insulin

Abstract: X-ray analysis, circular dichroism, receptor binding and biological potencies of chemically modified insulins suggest that the conformation of the insulin molecule is critical to the formation of both the zinc insulin hexamer and the insulin–receptor complex. Results are consistent with an insulin receptor-binding region including many of the hydrophobic residues important to dimerisation in addition to more polar surface residues. There is a further possibility of formation of an antiparallel sheet structure between the insulin and receptor molecules in the complex similar to that between monomers in the insulin dimer.

Overshadowing and stimulus intensity

Abstract: Two experiments on conditioned suppression in rats examined overshadowing between visual and auditory components of a compound conditioned stimulus. In the first experiment, when one component was markedly more salient than the other, the more salient overshadowed the less salient, but the latter, although acquiring significant associative strength, did not overshadow the former. When the two components were of approximately equal salience, each overshadowed the other. In the second experiment, reciprocal overshadowing was again observed between two equally salient stimuli, but only when their absolute intensities were relatively low. The failure to observe reciprocal overshadowing under all conditions raises problems for those theories of stimulus selection which assume that stimuli compete for some strictly limited resource. It was suggested, instead, that overshadowing might occur when animals fail to learn to attend to, or actually learn to ignore, stimuli that are not uniquely successful predictors of reinforcement.

A novel approach to Striga and Orobanche control using synthetic germination stimulants

Abstract: Summary: A series of synthetic germination stimulants for the plant parasites Striga and Orobanche has been prepared. These compounds, analogues of the natural Striga germination stimulant, strigol (I), (Cook et al., 1966, 1972) cause signiticant germination of Striga hermonthica (Del.) Benth. seed at concentrations as low as 10−9 M, and an even greater activity against species of Orobanche has been demonstrated. Initial outdoor box trials of the compounds against Striga asiatica (L.) O. Ktze. in Hyderabad, India, have shown a reduction of up to 65% of the seed after a single treatment of the soil 6 weeks before the planting of the sorghum host. Resume: Une possibilite nouvelle de lutte contre les Striga et les Orobancbe par l'utilisation des stimulants synthetiques de la germination. Une serie de stimulants syntbetiques de la germination pour les plantes parasites Striga et Orobanche ont ete prepares. Ces composes, analogues au stimulant naturel de la germination chez les Striga, le strigol (I), (Cook et al., 1966,1972) ont provoque une germination significative des semences de Striga hermonthica (Del.) Benth. a des concentrations aussi faibles que 10−9 M; une activite superieure a meme ete demontree sur des espeices d'Orobanche. Les premiers essais en pots, a l'exterieur, de ces composes contre Striga asiatica (L.) O. Ktze, a Hyderabad en Inde, ont montre une reduction atteignant 65% des semences aprees un seul traitement du sol, 6 semaines avant la plantation du sorgho, hote de ces plantes parasites. Zusammenfassung Ein neuartiger Weg in der Bekampfung von Striga und Orobanche durch die Anwendung synthetischer Keimungsstimulan-tien Es wurde eine Reihe von synthetischen Keimungsstimulantien fur die Pflanzenparasiten Striga und Orobanche hergestellt. Diese Verbindungen, Analoge des naturlichen Keimungsstimulans von Striga, Strigol (I), (Cook et al., 1966, 1972) bewirken bei so niedrigen Konzentrationen wie 10−9 M, eine beachtliche Keimung der Samen von Striga hermonthica (Del.) Benth. Fur Orobanche-Arten wurde sogar noch eine grossere Aktivitat nachgewiesen. Es wurden erste Gefass-versucbe mit diesen Verbindungen gegen Striga asiatica (L.) O. Ktze. in Hyderabad, Indien durcbgefuhrt. Dabei konnte bei einmaliger Behandiung des Bodens, 6 Wocben vor der Aussaat der Wirtspflanze (Hirse), ein Ruckgang der Samenzahl bis zu 65% festgestellt werden.

Use of a simplified fluctuation test to detect low levels of mutagens

Abstract: As a mutagen screening procedure we have used a modification of the Luria and Delbruck fluctuation test in which the individual tubes are scored by eye for the presence or absence of a mutation. The test is simple and extremely sensitive, detecting concentrations of mutagens up to 100-fold lower than conventional tests. Measuring mutation to tryptophan independence in Escherichia coli strain WP2 we have found that methyl methanesulphonate (0.5 μg/ml), mitomycin C (0.0015 μg/ml), dichlorvos (5 μg/ml, and K 2 CrO 4 (0.5 μg/ml) are all positively mutagenic in the test, whereas NiCl 2 is negative. Chronic exposure to low levels of mutagens using this method appears to induce more mutations than might be predicted by extrapolation from short exposure experiments at higher doses. The procedure is applicable to any system which involves mutation to prototrphy from a non-leaky auxotrophic requirement and should prove valuable in detecting and investigating the effects of low doses and chronic exposures.

Finding Picture Edges Through Collinearity of Feature Points

Abstract: The recovery of straight picture edges from digitizations of scenes containing polyhedra ("line finding") is central to the functioning of scene analysis programs. While recognizing that recovery properly involves a computational mobilization of a great deal of knowledge-supported context, there remain some basic issues of representation which govern the way in which the primary data—grey levels—are addressed. The paper describes a parametric representation of straight picture edges and its procedural deployment in the recovery of edges from digitizations of scenes whose contents are essentially polyhedra with strong visible shadows.

Short term screening tests for carcinogens.

Abstract: There are now short term tests with a high predictive value for mammalian carcinogens. Many of them are based on the ability to detect damage to DNA in bacteria or mammalian cells after metabolic activation by microsomal enzymes. Their introduction will enable provisional safety assessments to be made for the many thousands of industrial and environmental chemicals for which long-term animal testing cannot at present be considered.

Recombination modification in a fluctuating environment

Abstract: This paper examines the theory of the evolution of increased recombination between two loci subjected to interactive selection in a temporally fluctuating environment. Both cyclical and stochastic environments are considered. It is shown that temporal variation in the linkage disequilibrium coefficient for the pair of selected loci, due to fluctuations in the selective values of the genotypes at these loci, can give rise to selection in favor of modifier genes increasing recombination. The equilibrium level of recombination established in a given population depends on several factors; it is highest for intermediate values of the environmental periodicity or autocorrelation, for cases when the modifier genes are themselves closely linked to the selected loci, and for high levels of environmental variation. In general, it seems that the rate of modification of recombination values by this process will be low except when the modifiers are tightly linked to the selected loci. The possible evolutionary significance of this process is discussed in relation to observations on genetic systems of plants and animals.

The Effect of Memory Load on the Circadian Variation in Performance Efficiency Under a Rapidly Rotating Shift System

Abstract: Experimental shift work studios have typically found body temperature and performance efficiency to show very similar circadian rhythms. However, the performance tasks used have placed little, if any, reliance on short term memory. Studies of the variation in performance during the normal waking day have found performance on most tasks to improve over the day but that on short term memory tasks to decrease. The present paper reports an experimental study of the performance of two subjects on a rapidly rotating (-2-2) shift system. Three versions of a now performance test, each with a different memory load, wore administered four times per shift. With the low memory load version, performance showed a high positive correlation with body temperature and was poor during the night shift. However, with the high memory load version, performance was negatively correlated with temperature and was best during the night shift. It is concluded that future shift work studies must take into account the memory load of t...

The Tail Movements of Ungulates, Canids and Felids With Particular Reference To Their Causation and Function as Displays

Abstract: This paper describes the tail movements of ungulates, canids and felids, and the situations which elicit them. In this way the cause and function of tail movements for communication are considered. Tail movements can be divided into dorso-ventral (that is elevation and depression) which are closely associated with changes in postural tonus, and lateral tail movements (tail wagging). These tail movements are reported in detail in pigs, cattle, horses, goats, dogs and cats, together with the contexts that give rise to them. Information from personal observations and the literature in a number of other species is also reported. It is found that tail elevation and a high postural tonus are correlated and indicate a preparation for locomotion, and an increase in pace. In this way upright postures have become of communicative value to indicate a preparation for locomotion, alertness and thus warning. They are also used in confident approach and ofen associated with aggressive intentions. In some species this posture has become exaggerated specifically, to increase its signal value. A drop in postural tonus is shown to be related to fear. Postures of low tonus, combined often with a protective withdrawal of the tail and ears, are characteristic of fearful situations and have therefore become of signal value indicating fear and in social contexts, non-aggression and submission. Exaggeration of these postures is evident in some species. Lateral tail movements originated in association with locomotion (e.g., in fish). It is shown that there is still an association of lateral tail movements with locomotion in the mammals considered, although this is often particularly evident where locomotion is frustrated or inhibited. Cutaneous stimulation has become particularly important in eliciting lateral tail movements in some species. It is shown both from observational and experimental data, that lateral tail movements tend to occur particularly in approach/avoidance conflict and frustrating situations. Lateral tail movements have much in common in cause with preening movements in birds, head shaking and ear flicking which have been shown to occur as transitional activites between bouts of ongoing behaviour. In some cases tail wagging, like preening in birds, has become exaggerated and its association with the above situations ensures that a message is transferred by it with information about the communicators general motivational state. However sometimes it is also associated with a more specific message (e.g., tail wagging as an intention to kick in the horse, or as an indicator of non-aggression and 'friendliness" in the dog). An increase in postural tonus and tail wagging occur in many different situations. What all of them have in common is that the animal is 'excited'. This is defined and it is suggested that 'excitement' could be a useful descriptive term. Thus a common causal model is proposed for the elevation, depression and lateral movements of the tail in ungulates, canids and felids. Although there has been an emphasis in some species on particular types of tail movements in specific situations for use as visual signals, nevertheless most movements of the tail in these widely differing species can be shown to be associated with locomotion, only lateral movements are, in some species also associated wih cutaneous irritation. There is no evidence to suggest however that there has been an emancipation of causation, although some tail movements are exaggerated and otherwise ritualized.

Construction of a P plasmid carrying nitrogen fixation genes from Klebsiella pneumoniae.

Abstract: THE wide host range of plasmids of the P-incompatibility class1,2 has attracted interest in this group of R factors. A 3×106-dalton sequence which includes the TEM β-lactamase gene found on some plasmids of this group can integrate into the Escherichia coli chromosome3 and into plasmids of other compatibility groups1,4,5. This translocatable sequence has been termed transposon A (TnA)4,6 and resembles the insertion sequences (IS) of E. coli, in that TnA insertions can result in gene inactivation, giving rise to strong polar mutations7.

Perception of melodies

Abstract: A computer program has been written which will transcribe a live performance of a classical melody into the equivalent of standard musical notation. It is intended to embody, in computational form, a psychological theory of how Western musicians perceive the rhythmic and tonal relationships between the notes of such melodies.

The Organization of Aggression and Fear In Vertebrates

Abstract: This chapter considers what factors influence the occurrence of attack and fear behavior (e.g., immobility, flight, distress signals). It is argued that, with the exception of conditioned attack and fear behavior, the same types of basic situations are capable of evoking either type of response.

Theoretical study of the O(1D) + H2(1Σ g +) reactive quenching process

Abstract: Classical trajectory calculations have been made for the system O(1 D) + H 2(1Σ g +) →OH(2Π) + H(2 S) using an analytical singlet ground state surface for H 2O. A rate constant of 1·73 × 10-10 cm3 molecule-1s-1 at 300 K has been obtained. The distribution of energy in the products is approximately 30 per cent in translation, 45 per cent in vibration and 25 per cent in rotation. Because of the preponderance of vibrationally long-lived trajectories, statistical theories gave a good interpretation of the gross features of the reaction.

Inhibition by acetylene of conventional hydrogenase in nitrogen-fixing bacteria

Abstract: ONE of the earliest observations associated with nitrogen fixation was that all nitrogen-fixing organisms contained hydrogenase and nitrogenase1. We show here that acetylene, which is widely used as a substrate for nitrogenase, inhibits conventional hydrogenase activity and thus prevents the uptake of H2 formed by nitrogenase in the presence of CO. Our evidence also suggests that azotobacter nitrogenase forms H2 in vivo and that hydrogenase reoxidises this H2 to provide reducing power for metabolism.

Light, and photoreceptor degeneration in the Norway lobster, Nephrops norvegicus (L.)

Abstract: The visual pigment of Nephrops norvegicus (L.), the Norway lobster, was measured microspectrophotometrically in isolated rhabdoms, and found to have a $\lambda \_{\max}$ at 498 nm. On exposure to light this pigment changed into a long-lived photoproduct of $\lambda \_{\max}$ 484 nm (and higher maximal extinction) which broke down slowly in the dark. The bleaching process affected the structural stability of the rhabdoms, resulting in their progressive degeneration. These in vitro effects were found to occur also in vivo by exposing lobsters, caught and maintained in darkness, to low-level illumination from a single fluorescent tube. Exposure of only 2.5 h duration was enough to cause complete degeneration of the rhabdoms within 24 h even though the animals were thereafter kept in darkness. It is suggested that this effect of light is a consequence of the rapid build-up of photoproduct in a species having a low regeneration rate of the visual pigment. When the major part of the visual pigment is in the thermally less-stable, bleached state, the structural integrity of the photoreceptor is affected, leading to degeneration. This type of degeneration might be induced in other 'dim light' species (e.g. deep-sea fishes) that may also have low rates of pigment regeneration.