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We report a novel molecular ruler for measurement of distances and distance distributions with accurate external calibration. Using solution X-ray scattering we determine the scattering interference between two gold nanocrystal probes attached site-specifically to a macromolecule of interest. Fourier transformation of the interference pattern provides a model-independent probability distribution for the distances between the probe centers-of-mass. To test the approach, we measure end-to-end distances for a variety of DNA structures. We demonstrate that measurements with independently prepared samples and using different X-ray sources are highly reproducible, we demonstrate the quantitative accuracy of the first and second moments of the distance distributions, and we demonstrate that the technique recovers complex distribution shapes. Distances measured with the solution scattering-interference ruler match the corresponding crystallographic values, but differ from distances measured previously with alternate ruler techniques. The X-ray scattering interference ruler should be a powerful tool for relating crystal structures to solution structures and for studying molecular fluctuations.

Methane, a carbon source for methanotrophic bacteria, is the principal component of natural gas and is produced during anaerobic digestion of organic matter (biogas). Methanotrophs are a viable source of single cell protein (feed supplement) and can produce various products, since they accumulate osmolytes (e.g. ectoine, sucrose), phospholipids (potential biofuels) and biopolymers (polyhydroxybutyrate, glycogen), among others. Other cell components, such as surface layers, metal chelating proteins (methanobactin), enzymes (methane monooxygenase) or heterologous proteins hold promise as future products. Here, scenarios are presented where ectoine, polyhydroxybutyrate or protein G are synthesised as the primary product, in conjunction with a variety of ancillary products that could enhance process viability. Single or dual-stage processes and volumetric requirements for bioreactors are discussed, in terms of an annual biomass output of 1000 tonnesyear(-1). Product yields are discussed in relation to methane and oxygen consumption and organic waste generation.

Cortical evoked potentials to light flashes of 4 intensities and performances on a kinesthetic figural after-effects perceptual task (KFA) were obtained from normal and nonparanoid schizophrenic subjects. In previous studies it had been shown that individual differences in perception of stimulus intensity could be inferred from KFA performance. In this study, it was hypothesized that individuals whose KFA scores indicated a tendency to reduce the perceived intensity of strong stimulation would show a comparable response tendency on a cortical evoked response procedure. Significant correlations were found between evoked response latency and amplitude measures and KFA values in both normal and psychiatric groups. Sex differences in evoked response parameters were also found, males showing a steeper intensity-response function than females. Further, sex was found to be an important moderator variable of the relationship between evoked response measures and KFA values. These findings were interpreted in terms of a theoretical construct regarding a stimulus intensity control mechanism in the central nervous system. 1 N the associate author's recent paper on the schizophrenias, 10 a formulation was presented regarding a stimulus intensity control mechanism in the central nervous system. The purpose of this study is to demonstrate a neurophysiological basis for the formulation and to extend its application to sensory behavior studies of nonpsychiatric individuals. Based originally and in large part upon the work of Petrie and her colleagues, 9 -10 -u the stimulus intensity control hypothesis was aimed at reconciling two apparently contradictory kinds of findings in the literature on schizophre-

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