Search

A new self-gelating triterpenoid natural product has been isolated from the bark of the silver fir, Abies alba. The structure is desmethylabietospiran (3) on the basis of chemical and spectroscopic evidence. Also reported is a more efficient isolation procedure of abietospiran (1) from A. alba.

The genomes of the spirochaetes Borrelia burgdorferi and Treponema pallidum show strong strand-specific skews in nucleotide composition, with the leading strand in replication being richer in G and T than the lagging strand in both species. This mutation bias results in codon usage and amino acid composition patterns that are significantly different between genes encoded on the two strands, in both species. There are also substantial differences between the species, with T.pallidum having a much higher G+C content than B. burgdorferi. These changes in amino acid and codon compositions represent neutral sequence change that has been caused by strong strand- and species-specific mutation pressures. Genes that have been relocated between the leading and lagging strands since B. burgdorferi and T.pallidum diverged from a common ancestor now show codon and amino acid compositions typical of their current locations. There is no evidence that translational selection operates on codon usage in highly expressed genes in these species, and the primary influence on codon usage is whether a gene is transcribed in the same direction as replication, or opposite to it. The dnaA gene in both species has codon usage patterns distinctive of a lagging strand gene, indicating that the origin of replication lies downstream of this gene, possibly within dnaN. Our findings strongly suggest that gene-finding algorithms that ignore variability within the genome may be flawed.

Gas is New Zealand's major thermal fuel for electricity generation. This paper describes what influences the volumes of gas burnt by ECNZ, and forecasts future gas demands for electricity generation. It also reviews the uncertainties associated with these forecasts and likely competition in building new electricity generating stations and outlines the strategy now being formulated to accommodate them. Because ECNZ's generation system is hydro-based, relatively small rapid changes in hydrological conditions can significantly affect the amount of gas used. This situation will change over time with major increases in thermal generation likely to be needed over the next 20 years. However, there are considerable uncertainties on gas supply and electricity demand levels in the long run, which will complicate investment and fuel decisions.

The major spore coat proteins (SP60, SP70, and SP96) of Dictyostelium discoideum have been analyzed by using two-dimensional nonequilibrium pH gradient electrophoresis. These proteins have been characterized with respect to electrophoretic behavior, metachromatic staining with silver, and posttranslational modifications; these techniques allow unambiguous identification of these proteins in silver-stained gels and autofluorograms of total cell extracts. They are synthesized by cells in the prespore region of migrating slugs, ultimately becoming major components of mature spores, but are not detectable either in cells in the prestalk region of slugs or in mature stalk cells. The ease with which these relatively abundant proteins can be recognized on two-dimensional gels makes them very useful markers for spatial and temporal differentiation in this organism.

A number of zidovudine phosphoramidate and phosphorodiamidate derivatives were prepared, including some previously unreported benzyl esterified amino acyl compounds. These were found to be active in vitroagainst the human immunodeficiency virus (HIV-1), and were tested subsequently in the S+L-tissue culture assay against urethane leukaemia virus (ULV), a murine leukaemia virus (MuLV). The fifteen compounds tested showed a similar range of activity against the two viruses. No active compounds were missed in the MuLV system which was usually more sensitive to antiviral effects. Five compounds showed some toxicity to the mouse cells only. We are using this system in parallel with HIV assays to identify those derivatives which will be tested subsequently against a murine retrovirus in vivo.

A cryptic plasmid, pBAA1, was identified in an industrial Bacillus strain. The plasmid is 6.8 kilobases in size and is present in cells at a copy number of approximately 5 per chromosome equivalent. The plasmid has been maintained under industrial fermentation conditions without apparent selective pressure and so is assumed to be partition proficient. The minimal replicon was localized to a 1.4-kilobase fragment which also contains the functions required for copy number control. The very low level of segregational instability of the minimal replicon suggests that it also contains functions involved in plasmid maintenance. Comparison with other plasmids indicates that pBAA1 belongs to the group of small gram-positive plasmids which replicate by a rolling cycle-type mechanism. A sequence was identified which is required for the efficient conversion of the single plus strand to the double-stranded form during plasmid replication. Deletion of this sequence resulted in a low level of segregational plasmid instability.

The sensitivity of Bacillus subtilis to hydrogen peroxide (oxidative stress) was found to vary with the position of the culture in the growth cycle. The most dramatic change occurred at the stationary phase, when the cells became totally resistant to 10 mM H2O2, in contrast to the loss of 3 to 4 log units of viability when treated at the early log phase. Two of the eight proteins induced by a protective concentration of H2O2 (50 muM) were also induced (in the absence of oxidative stress) on entry into the late log phase of growth. The response of five isogenic spo0 mutants (spo0B, spo0E, spo0F, spo0H, and spo0J) to oxidative stress was identical to that of the wild-type parental strain. In an isogenic spo0A strain, mid-log-phase cells were 100-fold less sensitive to 10 mM H2O2 than was the wild type. Pretreatment with 50 microM H2O2 induced little further protection, suggesting that the response is constitutive in this strain. By comparison of proteins induced by 50 microM H2O2 in the wild-type, spo0A, spo0H, and spo0J strains, four proteins were identified that may be essential for protection against lethal concentrations of H2O2. The presence of multiple copies of the spo0H gene in a spo0A background converted the stress phenotype of the spo0A mutant to that of the wild type but left the sporulation phenotype unaltered.

Pretreatment of Bacillus subtilis with low concentrations of hydrogen peroxide protected the cells against the lethal effects of higher levels of oxidative stress. During the period of adaptation, eight proteins were induced, as detected by one-dimensional gel electrophoresis. Four of these proteins were the same size as four of the proteins induced by the temperature upshift. The range of proteins synthesized in response to an elevation in temperature depended both on the starting (lower) temperature and on the temperature to which the cells were shifted. Both catalase and superoxide dismutase were present at high levels in B. subtilis, but neither was induced by oxidative stress or temperature upshift. In fact, catalase activity was reduced after the temperature upshift.