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The effect of illumination on alertness can be assessed by comparing the efficacy of an anesthetic under light vs. dark conditions. Results from such tests on wild-type flies and visual mutants demonstrate that, surprisingly, light has both positive and negative influences on arousal. These dual effects may explain aspects of the fly's daily activity and have potential clinical implications.

In addition to their well-known effects on the development of the mushroom body, mud mutants are also female sterile. Here we show that, although the early steps of ovmT development are grossly normal, a defect becomes apparent in meiosis II when the two component spindles fail to cohere and align properly. The products of meiosis are consequently mispositioned within the egg and, with or without fertilization, soon undergo asynchronous and spatially disorganized replication. In wild-type eggs, Mud is found associated with the central spindle pole body that lies between the two spindles of meiosis II. The mutant defect thus implies that Mud should be added to the short list of components that are required for the formation and/or stability of this structure. Mud protein is also normally found in association with other structures during egg development: at the spindle poles of meiosis I, at the spindle poles of early cleavage and syncytial embryos, in the rosettes formed from the unfertilized products of meiosis, with the fusomes and spectrosomes that anchor the spindles of dividing cystoblasts, and at the nuclear rim of the developing oocyte. In contrast to its important role at the central spindle pole body, in none of these cases is it clear that Mud plays an essential role. But the commonalities in its location suggest potential roles for the protein in development of other tissues.

A critical factor in visual function is the speed with which photoreceptors (PRs) return to the resting state when light intensity dims. Several elements subserve this process, many of which promote the termination of the phototransduction cascade. Although the known elements are intrinsic to PRs, we have found that prompt restoration to the resting state of the Drosophila electroretinogram can require effective communication between the retina and the underlying brain. The requirement is seen more dramatically with long than with short light pulses, distinguishing the phenomenon from gross disruption of the termination machinery. The speed of recovery is affected by mutations (in the Hdc and ort genes) that prevent PRs from transmitting visual information to the brain. It is also affected by manipulation (using either drugs like neostigmine or genetic tools to inactivate neurotransmitter release) of cholinergic signals that arise in the brain. Intracellular recordings support the hypothesis that PRs are the target of this communication. We infer that signaling from the retina to the optic lobe prompts a feedback signal to retinal PRs. Although the mechanism of this retrograde signaling remains to be discerned, the phenomenon establishes a previously unappreciated mode of control of the temporal responsiveness of a primary sensory neuron. acetylcholine | electroretinogram | general anesthetics | photoreceptor

The integration host factor-deoxyribonucleic acid (IHF-DNA) complex is a minor groove-intercalating DNA-bending protein. Analysis of the crystal structure of the Escherichia coli IHF-DNA complex indicated the presence of a pseudocontinuous helix of DNA that is wrapped around the protein. The DNA also forms a U-turn around the IHF which results in the formation of a complex pseudo-2 fold symmetry by both components in the complex protein.

The Escherichia coli IHF protein is a heterodimer which binds to consensus sequences at attachment sites, the region of lambda integration and excision. The proposal that IHF functions to deform DNA during excision recombination was tested. The results showed that two different agents that deform DNA, HU and A tracts, could at least partially replace IHF during excisive recombination. In addition, the addition of sequence-directed bends to both attL and attR could result in a significant level of recombination in the absence of host factors. These results strengthen the hypothesis that IHF is an architectural element.

A study was done on the symmetry in the mechanism of bacteriophage lambda integrative recombination. Results have shown that a nucleophile from the recombinase Int attacks the phosphodiesterase backbone during both top- and bottom-strand exchange events in the two attachment sites for integrative recombination. Both phosphodiesters proceed through a covalent protein-DNA intermediate during strand exchange.