mlt Mutants of polyoma virus

New mlt deletion mutants of polyoma virus were isolated, and their abilities to produce a lytic response in mouse cells or to transform rat cells were assessed. Their properties were analyzed in terms of the sequences deleted and their effects upon the structure and functions of the viral middle and large T-antigens.     

Protein kinase activities associated with distinct antigenic forms of polyoma virus middle T-antigen

The tyrosine-specific protein kinase activity previously described in T-antigens of polyoma virus immunoprecipitated with anti-tumour sera has been investigated using monoclonal antibodies. This activity is associated with middle T-antigen but it can be separated by selective antibody precipitation from the majority of this protein. The difference between active and inactive forms can be accounted for by an antigenic difference at the N terminus of middle T-antigen molecules. Moreover, the two different mol. wt. forms of middle T-antigen that can act as phosphoacceptors have been separated by antibody precipitation and therefore shown to be immunologically distinct. The binding position of the antibody used for immunoprecipitation has been observed to have a quantitative influence on the in vitro protein kinase reaction, in one case appearing to stimulate the activity. The detection of the in vitro protein kinase activity in immunoprecipitates obtained with several different monoclonal antibodies directed against the middle T-antigen indicates that the activity is a property tightly associated with this polyoma virus-coded protein.     

Evaluation of the role of AMP-activated protein kinase and its downstream targets in mammalian hibernation

Mammalian hibernation requires an extensive reorganization of metabolism that typically includes a greater than 95% reduction in metabolic rate, selective inhibition of many ATP-consuming metabolic activities and a change in fuel use to a primary dependence on the oxidation of lipid reserves. We investigated whether the AMP-activated protein kinase (AMPK) could play a regulatory role in this reorganization. AMPK activity and the phosphorylation state of multiple downstream targets were assessed in five organs of thirteen-lined ground squirrels (Spermophilus tridecemlineatus) comparing euthermic animals with squirrels in deep torpor. AMPK activity was increased 3-fold in white adipose tissue from hibernating ground squirrels compared with euthermic controls, but activation was not seen in liver, skeletal muscle, brown adipose tissue or brain. Immunoblotting with phospho-specific antibodies revealed an increase in phosphorylation of eukaryotic elongation factor-2 at the inactivating Thr56 site in white adipose tissue, liver and brain of hibernators, but not in other tissues. Acetyl-CoA carboxylase phosphorylation at the inactivating Ser79 site was markedly increased in brown adipose tissue from hibernators, but no change was seen in white adipose tissue. No change was seen in the level of phosphorylation of the Ser565 AMPK site of hormone-sensitive lipase in adipose tissues of hibernating animals. In conclusion, AMPK does not appear to participate in the metabolic re-organization and/or the metabolic rate depression that occurs during ground squirrel hibernation.     

A limited survey of aflatoxins and fumonisins in retail maizebased products in the UK using immunoassay detection

A total of 27 maize-based products destined for human consumption were collected from retail outlets within the city of Glasgow in the UK and were analysed for the presence of aflatoxins using immunoaftinity column chromatography with fluorescence detection and for fumonisins by competitive ELISA. Aflatoxins were detected at a trace level below 4 in eight (30%) of the 27 samples tested, no sample contained aflatoxins at a high level although one sample of sweetcorn did contain aflatoxins at a level of 5-10 Fumonisins were detected in eight (30%) of the samples at levels from 1 to 8mgkg^-1 and a further eight samples contained fumonisin at a level below 1 mgkg^-1 but above the detectable level. The highest concentration of fumonisins was found in a sample of fine corn meal at 8-12mgkg^-1.     

The spatial scale of variability in small-mammal populations

We studied small-mammal populations across a range of spatial scales to determine which scales were relevant to demographic variability. We predicted that a scale of variability in population structure would occur at the scale of dispersal, which has previously been described as < 200 m for some small-mammal species. Systematic live-trapping surveys were conducted on nested grids at three scales: 1) extent = 4900 ha. grain =1000 m; 2) extent = 306 ha, grain = 250 m: and 3) extent = 31 ha. grain = 125 m. Prior to the present study, small-mammal populations had not been systematically live-trapped across a similar range of scales. From 1996 to 1998, surveys were conducted on a landscape intensively managed for timber, and on a reference landscape. Spatial analysis of abundance data demonstrated that small-mammal populations (four species) exhibited positive spatial autocorrelation at distances of between 133 and 533 m depending on the species and the landscape. No higher-order population structure was detected. Thus, within the range of scales we sampled, variability in small-mammal abundance occurred over short distances (i.e. 133–533 m).