Two Ozma problems are defined. Parity nonconservation is necessary for their solutions. Both problems may be solved by beta decay or atomic optical activity. Atomic and molecular sum frequency generation is chosen, as it supplies rich methods of effecting "gedanken" solutions to the Ozma problems. A new method of measuring a parameter manifesting molecular parity violations is advanced.

We introduce a method for optically imaging intracellular proteins at nanometer spatial resolution. Numerous sparse subsets of photoactivatable fluorescent protein molecules were activated, localized (to approximately 2 to 25 nanometers), and then bleached. The aggregate position information from all subsets was then assembled into a superresolution image. We used this method–termed photoactivated localization microscopy–to image specific target proteins in thin sections of lysosomes and mitochondria; in fixed whole cells, we imaged vinculin at focal adhesions, actin within a lamellipodium, and the distribution of the retroviral protein Gag at the plasma membrane.

Commentary: The original PALM paper by myself and my friend and co-inventor Harald Hess, spanning the before- and after-HHMI eras. Submitted and publicly presented months before other publications in the same year, the lessons of the paper remain widely misunderstood: 1) localization precision is not resolution; 2) the ability to resolve a few molecules by the Rayleigh criterion in a diffraction limited region (DLR) does not imply the ability to resolve structures of arbitrary complexity at the same scale; 3) true resolution well beyond the Abbe limit requires the ability to isolate and localize hundreds or thousands of molecules in one DLR; and 4) certain photoactivatable fluorescent proteins (PA-FPs) and caged dyes can be isolated and precisely localized at such densities; yielding true resolution down to  20 nm. The molecular densities we demonstrate (105 molecules/m2) are more than two orders of magnitude greater than in later papers that year (implying ten-fold better true resolution) – indeed, these papers demonstrate densities only comparable to earlier spectral or photobleaching based isolation methods. We validate our claims by correlative electron microscopy, and demonstrate the outstanding advantages of PA-FPs for superresolution microscopy: minimally perturbative sample preparation; high labeling densities; close binding to molecular targets; and zero non-specific background.

Metal ion homeostasis is critical to the survival of all cells. Regulation of nickel concentrations in Escherichia coli is mediated by the NikR repressor via nickel-induced transcriptional repression of the nickel ABC-type transporter, NikABCDE. Here, we report two crystal structures of nickel-activated E. coli NikR, the isolated repressor at 2.1 A resolution and in a complex with its operator DNA sequence from the nik promoter at 3.1 A resolution. Along with the previously published structure of apo-NikR, these structures allow us to evaluate functional proposals for how metal ions activate NikR, delineate the drastic conformational changes required for operator recognition, and describe the formation of a second metal-binding site in the presence of DNA. They also provide a rare set of structural views of a ligand-responsive transcription factor in the unbound, ligand-induced, and DNA-bound states, establishing a model system for the study of ligand-mediated effects on transcription factor function.

Auditory feedback is critical for the development and maintenance of speech in humans. In contrast, studies of nonhuman primate vocal production generally report that subjects show little reliance on auditory input. We examined the extent to which cotton-top tamarin (Saguinus oedipus) vocal production is sensitive to perturbation of auditory feedback by manipulating the predictability of presentation of a 1 s burst of white noise during the production of the species-specific contact call, the combination long call (CLC). We used three experimental conditions: the Begin condition, in which white noise was presented only during the first half of a recording session, the End condition, in which white noise was presented only in the last half, and the Random condition, in which each call had a 50% probability of receiving white noise playback throughout the recording session, making the auditory feedback unpredictable. In addition we recorded calls before and after the experimental series (Baseline condition) to determine whether any changes induced by modification of auditory feedback persisted. Results showed that playback of white noise during the production of the CLC produced changes in the temporal structure of the CLC: calls were shorter and had fewer pulses, indicating that modification of auditory feedback can interrupt vocal production. In addition, calls that received modified feedback were louder and had longer inter-pulse intervals than those that did not, consistent with an adaptive response to the masking effect of white noise playback. The magnitude of this compensatory effect and the interruption rate were both sensitive to whether the feedback modification occurred at the beginning or end of the experimental session: early feedback produced less interruption and more compensation. Finally, when auditory feedback modification was unpredictable, adaptive changes were observed in both calls that received modified feedback and those that received normal feedback, suggesting that tamarins can generate an expectation of noise playback and increase vocal amplitude in anticipation of masking.

Pyrroline-5-carboxylate reductase (P5CR) catalyzes the reduction of Delta1-pyrroline-5-carboxylate (P5C) to proline with concomitant oxidation of NAD(P)H to NAD(P)(+). The enzymatic cycle between P5C and proline is very important in many physiological and pathological processes. Human P5CR was over-expressed in Escherichia coli and purified to homogeneity by chromatography. Enzymatic assays of the wild-type protein were carried out using 3,4-dehydro-L-proline as substrate and NAD(+) as cofactor. The homopolymer was characterized by cross-linking and size exclusion gel filtration chromatography. Human P5CR was crystallized by the hanging-drop vapor-diffusion method at 37 degrees C. Diffraction data were obtained to a resolution of 2.8A and were suitable for high resolution X-ray structure determination.

Many species of insects display dispersing and nondispersing morphs. Among these, aphids are one of the best examples of taxa that have evolved specialized morphs for dispersal versus reproduction. The dispersing morphs typically possess a full set of wings as well as a sensory and reproductive physiology that is adapted to flight and reproducing in a new location. In contrast, the nondispersing morphs are wingless and show adaptations to maximize fecundity. In this review, we provide an overview of the major features of the aphid wing dimorphism. We first provide a description of the dimorphism and an overview of its phylogenetic distribution. We then review what is known about the mechanisms underlying the dimorphism and end by discussing its evolutionary aspects.