Populations of rodents were studied for periods of 7−9 years at each of three sites in arid Australia. All species fluctuated dramatically in abundance, being absent or in low numbers during droughts but erupting after significant rainfall. Strong correlations were obtained between capture rates and cumulative monthly rainfall residuals, with time lags, that had been modified by an exponential decay function to model the post-rain depletion of resources. The introduced Mus domesticus erupted within only two months of exceptional rainfall at one site, whereas the native rodents Notomys alexis, Pseudomys hermannsburgensis and P. desertor generally responded 3Œ10 months after rain. The faster response of M. domesticus reflects its high reproductive potential compared with the native rodents, and perhaps greater immigration. Differences in magnitudes and delays in response to rainfall among the native species were due probably to differences in initial population sizes and times available for response and, for P. desertor, to between-site differences in the quality or quantity of food resources. Population declines in all species during dry periods probably followed resource shortages. Despite the usually strong linkage between rainfall and population dynamics, rain failed to trigger population responses in rodents for prolonged periods at two of the sites, and was not clearly associated with an eruption of P. hermannsburgensis at the third. The lack of a population response at one site was attributed to predation, but events at the other two remain unexplained. We conclude that long-term studies should play an important role in describing temporal changes in rodent populations in arid Australia and, with field experiments, in evaluating how rainfall and other factors combine to effect the changes.

Feral cats (Felis catus) occur throughout central Australia. In this study, we analysed the stomach contents of 390 feral cats collected between 1990 and 1994 from the southern half of the Northern Territory. Cats fed on a wide variety of invertebrates, reptiles, birds and mammals, including animals up to their own body mass in size. Mammals were the most important prey but reptiles were regularly eaten in summer and birds were important in winter. Invertebrates were present in the diet in all seasons. Carrion appeared in stomach samples during dry winters only and this has implications for future control of feral cats.

We analyzed the effects of three different calcium concentrations on the RNA and functional protein levels of transglutaminase (TGase) and involucrin (INV) over time in culture. We compared the results in normal human keratinocytes with those in a squamous cell carcinoma, SCC4. The highest calcium concentration (1.2 mM) induced the greatest levels of INV and TGase message, INV protein, and rates of CE formation, but not maximal levels of TGase protein. By examining cytosol and membrane fractions of keratinocytes, we found that after synthesis, TGase protein shifts, under the influence of calcium (both 0.1 mM and 1.2 mM), from the cytosol into the membrane in postconfluent cells. However, only 1.2 mM calcium induced significant amounts of TGase activity. These data indicate that elevated calcium (1.2 mM) achieves the expected induction in keratinocyte differentiation by regulation of not only INV and TGase message levels, but also the translation and activation of TGase protein. Our data suggest that this calcium-induced activation of TGase protein occurs while the protein is anchored in the membrane. In contrast, despite ample INV and TGase message levels within SCC4 cells, these RNA levels are not regulated by calcium or translated into protein, suggesting that the transformed phenotype of SCC4 cells results not only in a failure of calcium to regulate gene transcription, but also in a defect within the translation machinery of these differentiation-specific proteins.

In general, prokaryotes are considered to be single-celled organisms that lack internal membrane-bound organelles. However, many bacteria produce proteinaceous microcompartments that serve a similar purpose, i.e. to concentrate specific enzymic reactions together or to shield the wider cytoplasm from toxic metabolic intermediates. In this paper, a synthetic operon encoding the key structural components of a microcompartment was designed based on the genes for the Salmonella propanediol utilization (Pdu) microcompartment. The genes chosen included pduA, -B, -J, -K, -N, -T and -U, and each was shown to produce protein in an Escherichia coli chassis. In parallel, a set of compatible vectors designed to express non-native cargo proteins was also designed and tested. Engineered hexa-His tags allowed isolation of the components of the microcompartments together with co-expressed, untagged, cargo proteins. Finally, an in vivo protease accessibility assay suggested that a PduD–GFP fusion could be protected from proteolysis when co-expressed with the synthetic microcompartment operon. This work gives encouragement that it may be possible to harness the genes encoding a non-native microcompartment for future biotechnological applications.

No abstract