RESUMEN
We performed comparative low temperature (2-30 K) hole-burning and single molecule experiments with 2-methylterrylene with the goal to detect single rotational tunneling jumps of methyl groups. The hole-burned spectrum with its sharply structured side features which are perfectly symmetrically arranged with respect to the central hole supports the assignment to rotational tunneling transitions. However, instead of one, three clearly distinguishable methyl groups show up in the spectrum. Based on molecular mechanics simulations we attribute them to different, nearly degenerate orientations of guest molecules in one specific site of the hexadecane lattice. The frequency distribution of spontaneous jumps of single molecules reflects the features of the hole-burned spectra, although the distribution in the single molecule experiments is significantly broader. The photoinduced frequency transformation of single molecules ("single molecule photobleaching experiments") fits to the features of the hole-burned spectra, except that, surprisingly, no significant number of spectral jumps could be generated in the frequency range where the prominent narrow antiholes are observed in the hole-burned spectra.
RESUMEN
The Drosophila gene optomotor-blind (omb) is involved in the development of a set of giant neurons in the optic lobes and possibly other structures in the imaginal brain. Adult flies have discrete defects in optomotor behavior. The gene has previously been mapped in chromomeres 4C5-6, together with three other genes, bifid, Quadroon and lacqueredgls. We have localized the gene in a genomic walk of 340 kb of DNA. By mapping seven chromosome breakpoints with omb phenotype we determined its minimum size to about 80 kb. From this region more than 20 RNAs of different size and temporal expression pattern are transcribed. Three of them (T3, T7 and T7') stem from primary transcripts of 40-80 kb in length. In its distal part the omb gene overlaps in at least 19 kb with four other complementation units, bifid, l(1)bifid, Quadroon and lacqueredgls. The three nonlethals affect the external appearance of the fly and seem to be unrelated to brain development.