Polycomb group (PcG) proteins function as high molecular weight complexes that maintain transcriptional repression patterns during embryogenesis. The vertebrate DNA binding protein and transcriptional repressor, YY1, shows sequence homology with the Drosophila PcG protein, pleiohomeotic (PHO). YY1 might therefore be a vertebrate PcG protein. We used Drosophila embryo and larval/imaginal disc transcriptional repression systems to determine whether YY1 repressed transcription in a manner consistent with PcG function in vivo. YY1 repressed transcription in Drosophila, and this repression was stable on a PcG-responsive promoter, but not on a PcG-nonresponsive promoter. PcG mutants ablated YY1 repression, and YY1 could substitute for PHO in repressing transcription in wing imaginal discs. YY1 functionally compensated for loss of PHO in pho mutant¯ies and partially corrected mutant phenotypes. Taken together, these results indicate that YY1 functions as a PcG protein. Finally, we found that YY1, as well as Polycomb, required the co-repressor protein CtBP for repression in vivo. These results provide a mechanism for recruitment of vertebrate PcG complexes to DNA and demonstrate new functions for YY1.

This work celebrates the "International Year of Chemistry -2011", by providing "for the first time", the structures at the atomic level of two important molecules, namely, ascorbic acid and aspirin. Ascorbic acid, also known as vitamin C, was discovered as a cure for scurvy which claimed many human lives and hence got its name. It is also supposed to be an antioxidant and to prevent flu. Aspirin is synthesized from salicylic acid and is widely used as a remedy for flu and has other medical uses such as saving the lives of cardiac patients as an anticoagulant of blood. The biochemistry and chemistry of both these compounds have been evolving for nearly a century ever since their discoveries. Here, the atomic structures of these compounds have been presented where the known lengths of the various chemical bonds are exact sums of the appropriate radii of the adjacent atoms.

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Eight single-copy DNA probes specific for human chromosome 3 were isolated by screening a human chromosome 3-derived genomic library. Southern blot analyses of DNAs isolated from a panel of somatic cell hybrids allowed us to regionally assign all probes to subregions on chromosome 3. Three clones were localized to the short arm of chromosome 3 (3p21→pter), two to the long arm (3q21→qter), and three to the 3q21→3p21 sub-region. Six of these DNA sequences map to regions overlapping a segment of chromosome 3 (3p14→p23) frequently deleted in small cell lung cancer cells. Restriction fragment length polymorphism analyses indicate that at least three of the eight single-copy probes studied show Msp1 or Bg/II polymorphisms. This library is a useful source of chromosome 3-specific probes.

Ten single-copy DNA probes derived from a human chromosome 3-specific genomic library were mapped by in situ hybridization to subregions of this chromosome. Seven sequences were assigned to subregions of 3q and two sequences were assigned to subregions of 3p. One single-copy DNA probe was assigned to the centromeric region of chromosome 3 by Southern blot analysis of DNA isolated from a somatic cell hybrid containing centromeric sequences of this chromosome. These DNA clones mapped by in situ hybridization can provide useful landmarks for mapping various disease loci on chromosome 3. They may also be useful for the generation of physical and genetic maps.