The polycistronic mRNA encoding the nine genes of the unc operon of Escherichia coli was studied. We demonstrated the ribosome-binding capabilities of six of the nine unc genes, uncB, uncE, uncF, uncH, uncA, and uncD, by using the technique of primer extension inhibition or "toeprinting." No toeprint was detected for the other genes, uncI, uncG, and uncC. The lack of a toeprint for uncG suggests that this gene is expressed by some form of translational coupling, such that either uncG is read by ribosomes which have translated the preceding gene, uncA, or translation of uncA is required for ribosome binding at the uncG site. RNA sequencing and primer extension in the regions of uncl and uncC, the first and last genes in the operon, respectively, gave less intense signals than those obtained for the other unc genes. This suggested that there are fewer copies of those regions of the transcript and that processing of the unc transcript occurred. Using primer extension and RNA sequencing, we identified sites in the unc transcript at which processing appears to take place, including a site which may remove much of the uncI portion of the transcript. Northern (RNA) blot analysis of unc RNA is consistent with the presence of an RNA-processing site in the uncl region of the transcript and another in the uncH region. These processing events may account for some of the differential levels of expression of the unc genes.The unc operon of Escherichia coli encodes the subunits of the proton-translocating ATPase, a membrane-bound enzyme complex capable of reversibly coupling translocation of protons across the plasma membrane to ATP synthesis or hydrolysis. This enzyme is similar in structure and function to enzymes of other bacteria, as well as to those of mitochondria and chloroplasts. Under aerobic conditions, it can synthesize ATP by using the electrochemical proton gradient generated by the electron transport chain, while they are produced in unequal amounts (2). These results, taken together, suggest that control at the level of translation is responsible for the differences in expression of the iinc genes.Statistical studies of codon usage indicate that there is a bias toward rare codon usage in unc genes (uncH, uncG, and uncC) that are expressed in low amounts (5, 11), as in other bacterial genes. This may play a part in the differential synthesis of the ATPase polypeptides, but other mechanisms are probably important as well.Several investigations have indicated that differences in rate of initiation of translation among the iinc genes account for much of the disparity in their levels of synthesis. It has been suggested that the presence of secondary structures in some intergenic regions of the uinc message affects translation of the subsequent genes by inhibiting ribosome binding (2). Computer predictions have indicated the presence of secondary structures before uncF, uncH, and uncG (16

The genome of the murine commensal strain Escherichia coli NGF-1 contains a 5.03-Mbp chromosome and plasmids of 40.2 kbp and 8.56 kbp. NGF-1 efficiently colonizes the mouse gut and is genetically tractable.

The present study aimed to investigate whether the perception of still scenes in a virtual environment in congruent versus incongruent condition can be influenced by odors. Ninety healthy participants were divided into three groups, including two experimental virtual reality (VR) environments: a rose garden, an orange basket, and a control condition. In each VR condition, participants were exposed to a rose odor, an orange odor, or no odor, resulting in congruent, incongruent, and control conditions. Participants were asked to describe (a) the content of the VR scene and rate its overall pleasantness and (b) the smell and to rate its intensity and pleasantness. For each condition, participants were tested twice. During the second test, participants provided ratings and descriptions of the content of the VR scenes without being exposed to odors or VR environments. Virtual scenarios tended to be remembered as more pleasant when presented with congruent odors. Furthermore, participants used more descriptors in congruent scenarios than in incongruent scenarios. Eventually, rose odor appeared to be remembered as more pleasant when presented within congruent scenarios. These findings show that olfactory stimuli in congruent versus incongruent conditions can possibly modulate the perception of the pleasantness of visual scenes but not the memorization.

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