Oligonucleotide dendrimers: stable nano-structures.

DNA dendrimers with two, three, six, nine or 27 arms were reassociated as complementary pairs in solution or with an array of complementary oligonucleotides on a solid support. In all cases, duplex stabilities were greater than those of unbranched molecules of equal length. A theoretical treatment for the process of dissociation of dendrimers explains the major properties of the complexes. The favourable features of DNA dendrimers-their enhanced stability and the simple predictability of their association behaviour-makes them promising as building blocks for the 'bottom up' approach to nano-assembly. These features also suggest applications in oligonucleotide array/DNA chip technology when higher hybridisation temperatures are required, for example, to melt secon-dary structure in the target.

On the mechanism of amplification of satellite II DNA sequences of the domestic goat Capra hircus.

A restriction enzyme analysis of the satellite II DNAs of the domestic goat Capra hircus, sheep Ovis aries and ox Bos taurus (p = 1.720, 1.723 and 1.722 g/cm3, respectively) has been carried out and shows that, although all three are composed of repeat units of 700 base-pairs, goat satellite II is present in the genome primarily in the form of 2100 base-pair trimers. Unequal crossing-over between repeat units has produced an oligomer series, whose oligomers gradually decrease in copy number the further they are in molecular weight from the trimer. The trimer population is much more uniform than the monomer population, as most trimers have similar restriction patterns, whereas their component monomers differ considerably in their restriction properties. This heterogeneity was confirmed by cross-hybridization of the different monomers of a cloned trimer. Here, heterologous hybrids were much less stable than the homologous hybrids. Attempts were made to simulate such an oligomer series by computer, using a longitudinal (saltatory), and two horizontal (unequal crossover and drive) models. Simulations of both the saltatory and drive mechanisms could produce the oligomer series in approximately the observed ratios, but only the former could simultaneously produce other restriction properties of this sequence family. This was because the other restriction sites were in a different (monomer) register, and it is difficult for a drive model promoting traits in only one register to fix properties in different registers. The unequal crossover model proposed by Smith (1973, 1976) generally produced homogeneous arrays from heterogeneous arrays, but higher-order repeat structures could be produced when the efficiency of crossing-over between different monomer types was reduced. In most of these arrays, the dimer was the predominant oligomer, but in approximately 10% the trimer was predominant. Since the unequal crossover model produces dimeric arrays with high frequency given appropriate conditions, it is an attractive model for explaining the production of satellite DNAs whose structure has evolved through a series of doublings, such as mouse major satellite DNA and the "alphoid" satellite sequences of primates. Other factors necessary for this model to work are generally considered to be natural components of the speciation process. It is therefore suggested that, although the saltatory model conforms most closely to the observed structure of goat satellite II, this particular satellite DNA may represent one of the few cases when the unequal crossover mechanism does not give rise to a dimeric structure.

Clonidine-induced hyperphagia in monkeys: evidence for alpha 2-noradrenergic receptor mediation.

The mechanism of clonidine-induced hyperphagia and weight gain in monkeys was studied in 11 Stumptail macaques. Clonidine induced a significant increase in food intake over baseline levels and a significant weight gain after the 3-day treatment period. Both changes induced by clonidine were antagonized by the alpha 2-noradrenergic antagonist yohimbine, but not by prazosin, an alpha 1-noradrenergic antagonist. These results suggest that clonidine-induced hyperphagia and weight gain in monkeys are mediated through alpha 2-noradrenergic receptors.

Detecting radiation damage to human chromosomes by flow cytometry.

The flow karyotype profile of ethidium bromide-stained chromosomes from human peripheral blood lymphocytes has been analysed following exposure of lymphocytes to graded series of X-ray doses in vitro. Flow analysis offers the potential for rapid counting of chromosome abnormalities and it is shown that the level of background fluorescence, the distribution of fluorescence and the area of peaks associated with the larger chromosomes, are altered in a dose-related fashion following previous exposures of cultured lymphocytes to 50-400 rad. Moreover, parallel manual analysis of the incidence of chromosome aberrations in metaphase samples of the irradiated cells show a close correlation between flow karyotype profile distortion and aberration frequency. It is estimated that for any given irradiated blood sample doses above 100 rad could be detected with certainty.

A functional computer recording system for a veterinary diagnostic laboratory.

The establishment of a computer system to process the diagnostic records of the veterinary laboratories of the Queensland Department of Primary Industries is described. A batch system is being used with an optical type input to an International Computers Limited computer. The reports are generated and then reduced photographically to standard size paper. The experience gained and the features and potential of the system are discussed including the particular advantages of the optical input system.

The prevalence and distribution of leptospiral titres in cattle and pigs in Queensland.

Serological test results for leptospiral species on serums from cattle and pigs performed by the diagnostic laboratories of the Queensland Department of Primary Industries from July 1973 to June 1976 were used to determine the prevalence and geographical distribution of 3 leptospiral serotypes in Queensland. There was a higher prevalence of antibodies to L. hardjo than to L. pomona in cattle, whereas in pigs the prevalence of antibodies to L. pomona was much higher than that for L. tarassovi or L. hardjo. Feral pigs had a particularly high prevalence of L. pomona antibodies. There is a different geographical distribution of antibodies to L. pomona and L. hardjo. L. hardjo antibodies appear to be fairly uniformly distributed but there is a higher prevalence of L. pomona antibodies in low rainfall areas. This relationship was shown to be significantly correlated.

Changes in cattle tick control practices in south eastern Queensland from 1977 to 1982.

Results of a survey of cattle producers in south eastern Queensland in 1982 concerning cattle tick control have been compared with those of a similar survey carried out in 1977-78. During the interval between these surveys the proportion of beef farms with tick resistant (Bos indicus infusion) cattle as the main breed had increased from 47.8% to 60.0%. Chemical control methods had improved but many producers were continuing to treat their cattle more often than necessary. Over the period there was an increase in the proportion of farms with small numbers of animals, and 30% of the farms had less than 50 cattle.

The significance of leptospiral titres associated with bovine abortion.

To investigate relationships between serological titres to 2 serovars, pomona (L. pomona) and hardjo (L. hardjo), of Leptospira interrogans and abortions, log linear and logit models were fitted to herd and individual cow data from cattle serologically negative for brucellosis. Serological titres to both serovars were significantly related to abortions in individual cows, with L. pomona having a stronger relationship than L. hardjo. L. hardjo was not significant when herd data were analysed. Differences between dairy and beef cattle in the serological titres found to both L. pomona and L. hardjo were detected when data sets of all cattle or cattle with no history of abortion were analysed. The beef/dairy differences may be due to different management practices and/or to different geographical distributions of both serovars and populations of beef and dairy cattle. If there are no cattle in a herd with a reciprocal titre of 3000 or greater for L. pomona, it is unlikely that L. pomona is associated with the abortion problem. There was no specific L. hardjo titre which separated high and low probabilities that the serum came from a cow or herd with an abortion history.

A survey concerning cattle tick control in Queensland. 2. Managerial aspects which indirectly affect tick control.

This paper reports those findings concerning property management from the 1977-78 survey of tick control in Queensland, which could effect efficient tick control and also presents a profile of the cattle industry in the tick infested areas at the time of the survey. The average property size was 400 hectares and the average number of cattle on the properties was 726.4. Larger properties tended to have crossbred Zebu cattle. The average number of paddocks per property was 7.2. The most popular stabilised crossbred Zebu breed was Santa Gertrudis but the most common type of cattle was crossbred Zebu, which was on 30% of properties. There were negligible numbers of crossbreed Zebu cattle on dairy properties. Control of other external parasites may result in additional dippings in areas where they occur. Although fence maintenance appears to be carried out regularly it is clear that the effectivness of tick control measures, such as pasture spelling and dipping which depend on clean musters, could be affected by the occurrence of fire, floods and other natural disasters on half the properties in the tick infested areas. There is no evidence from results in the survey that attention to other farming activities (mainly cropping) prevents producers from paying sufficient attention to tick control. In fact cropping often provides the opportunity for producers to rotate cattle around pastures. Producers appear to consider the cost of tick control is a burden and they expect assistance from the Government to reduce these costs. They do not appear to have considered how they can reduce the costs themselves.

A survey concerning cattle tick control in Queensland. 3. Chemical control.

Survey results concerning chemical control of the cattle tick (Boophilus microplus) in Queensland are reported in detail, and differences due to region, breed and type of enterprise are discussed. The results show that chemical control was more intensive in Zebu and Zebu crossbred cattle than could be justified economically and that a minority of producers with European cattle carried out strategic dipping. Owners of plunge dips did not make regular use of testing facilities, available from the Department of Primary Industries or the chemical companies.

A survey concerning cattle tick control in Queensland. 4. Use of resistant cattle and pasture spelling.

The results of a survey on tick control carried out in 1977-78 indicate that tick resistant cattle have been introduced for their heat and drought tolerance and their ability to grow more rapidly than European cattle, especially in the extensive grazing country of Northern and Central Queensland. In South-eastern Queensland acceptance of tick resistant cattle has been slower because producers believe they are more difficult to manage than European cattle. A need for more publicity to be given to the different handling methods required by these animals was shown. Some producers cull their less resistant crossbred Zebu cattle and others could be encouraged to do so. Pasture spelling appears to be quite common especially in the Costal North; it is being carried out for pasture management rather than as a tick control measure. Producers in Central and South-eastern Queensland, who do not spell pastures, feel that it reduces the carrying capacity.

Maximum entropy image reconstruction of DNA sequencing gel autoradiographs.

DNA sequencing gel autoradiographs become increasingly difficult to read as one moves up the gel, due to crowding and overlapping of the bands. Maximum entropy image reconstructions of the autoradiograph improve the ease with which crowded sequence data can be read, and extend the region of the gel in which reading is possible. Superior reconstructions are obtained by using nonuniform models based on the initial reconstructions.

Measurement of DNA length by gel electrophoresis II: Comparison of methods for relating mobility to fragment length.

Relationships between DNA length and electrophoretic mobility in an agarose gel have been compared by estimating the lengths of known DNA polymer fragments, using other fragments in the series as standards. Global estimates were made using 10 fragments as standards; local estimates were made using the two closest fragments on either side of the unknown as standards. Most relationships were fitted by least squares. All the relationships gave more accurate local than global estimates. The most accurate results were obtained using the reciprocal relationship, where the maximum error in the local estimates was less than 0.1%. The semilog relationship gave the least accurate results, with a maximum error in the local estimates of almost 5%. The polymer fragments were also used as standards to estimate the lengths of lambda DNA restriction fragments. Here the estimates were in error by up to 3%, indicating the influence of base composition and sequence on electrophoretic mobility.