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The temperate peatlands are extensive, covering around 3.5 million km2 of land. They contain about 455 Gt of carbon, almost equivalent to the carbon stored in all of the living things on the surface of the planet, and representing around 25% of all the soil carbon on earth. These bogs are a sink for atmospheric carbon and their carbon uptake accounts for about 12% of current human emissions. They vary considerably in their form and structure and are an important resource for scientific research, including the study of past environments and climate change, and they are also valuable in environmental education. They are low in biodiversity, but their fauna and flora are distinctive and many groups are confined to this habitat. For all these reasons, the future conservation of peatlands is a matter for concern. Threats to peatlands come from direct human exploitation in the form of peat harvesting for energy and horticulture, and drainage for forestry. Rising environmental awareness should control both of these processes in the western world, but continued northern peatland losses are likely locally, especially in Asia. Peatland drainage for forestry or agriculture will result in losses of carbon to the atmosphere, adding to the greenhouse effect. Human population pressures, industrialization and urbanization are unlikely to have an important direct and immediate influence in the boreal zone. Fragmentation of the habitat is not an important consideration because bogs are by their very nature ‘island’ habitats. Acidification by aerial pollution may be a local problem close to sources, but the habitat is naturally acid and should not be severely affected. The input of aerial nutrients, however, particularly nitrogen, could have widespread impact on bogs, enhancing their productivity and altering their vegetation composition. The physical rehabilitation of bogs damaged by human activities presents many problems, particularly relating to the re-establishment of peat structure and vegetation, but the process can result in the re-formation of a carbon sink so it is worth the effort. Climate change is the most important consideration in its impact on bogs. Higher temperature (especially if accompanied by raised atmospheric carbon dioxide levels and increased nitrate deposition) will enhance productivity, but will also result in faster decomposition rates. The outcome of these opposing factors for peat formation will ultimately depend on the future pattern of precipitation. If, as seems most likely, summer conditions become warmer and drier in continental regions and winters become milder and wetter, the summer drought could cause peat loss and bog contraction. An excess of decomposition will lead to bogs becoming a carbon source and thus a positive feedback in global warming. Emissions of methane and nitrous oxide would add to the greenhouse gas problem, but likely oxidation of methane and low N2O production may well mean that this impact will not prove to be significant. Tree invasion of bogs as a consequence of summer drought could locally lead to increased water loss through transpiration, and higher heat absorption through albedo change. This will enhance the drying effect on the bog surface. Oceanic mires will be less severely affected if the expected increase in precipitation takes place in these regions. The most important overall factor in determining the future of the northern bogs is likely to be the quantity and pattern (both spatially and temporally) of future precipitation in the zone.

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Tracts of the alternating dinucleotide polydeoxythymidylic-guanylic [d(TG)] polydeoxyadenylic-cytidylic acid [d(AC)], present throughout the human genome, are capable of readily forming left-handed Z-DNA in vitro. We have analyzed the effects of the Z-DNA motif d(TG)30 upon homologous recombination between two nonreplicating plasmid substrates cotransfected into human cells in culture. In this study, the sequence d(TG)30 is shown to stimulate homologous recombination up to 20-fold. Enhancement is specific to the Z-DNA motif; a control DNA fragment of similar size does not alter the recombination frequency. The stimulation of recombination is observed at a distance (237 to 1,269 base pairs away from the Z-DNA motif) and involves both gene conversion and reciprocal exchange events. Maximum stimulation is observed when the sequence is present in both substrates, but it is capable of stimulating when present in only one substrate. Analysis of recombination products indicates that the Z-DNA motif increases the frequency and alters the distribution of multiple, unselected recombination events. Specifically designed crosses indicate that the substrate containing the Z-DNA motif preferentially acts as the recipient of genetic information during gene conversion events. Models describing how left-handed Z-DNA sequences might promote the initiation of homologous recombination are presented.Homologous recombination is the process of exchange of genetic information between stretches of DNA containing sequence similarity. Although the degree of recombination is generally proportional to the length of homology, there are regions of DNA in which the rate of exchange is nonlinear with respect to distance, resulting in disparity between genetic and physical maps. The sequences responsible for this disparity, called "recombination hotspots," increase the rate of genetic exchange between homologous DNA molecules. The 8-base-pair (bp) Chi sequence in Escherichia coli is the most fully characterized recombination hotspot, shown to increase recombination in bacteriophage lambda and E. coli DNA via the RecA-RecBCD pathway (reviewed in reference 34). Recombination hotspots have also been described in fungi (12,25) and in mammalian cells (37; W. P. Wahls, L. J. Wallace, and P. D. Moore, Cell, in press).A short fragment of mammalian DNA from the human ,Bglobin gene cluster, MG-1 (29), promotes unusual recombination events during yeast meiosis (41). Molecular evidence indicates that the DNA sequence responsible is an 80-bp stretch of the simple repeating dinucleotide polydeoxythymidylic-guanylic polydeoxyadenylic-cytidylic acid, abbreviated hereafter as d(TG)n.The repeating dinucleotide d(TG)" is not detectable in the genomes of eubacteria, archaebacteria, or mitochondria (11) but is ubiquitously present in eucaryotic chromosomes (13,29,40). It is estimated that there are on the order of 105 copies of this dinucleotide repeat, each approximately 10 to 50 bp in length, scattered throughout the mammalian genome. A striking feature of these r...