Sergei Tillib

Trithorax- and Polycomb-group response elements within an Ultrabithorax transcription maintenance unit consist of closely situated but separable sequences.

ABSTRACT In Drosophila, two classes of genes, thetrithorax group and the Polycomb group, are required in concert to maintain gene expression by regulating chromatin structure. We have identified Trithorax protein (TRX) binding elements within the bithorax complex and have found that within thebxd/pbx regulatory region these elements are functionally relevant for normal expression patterns in embryos and confer TRX binding in vivo. TRX was localized to three closely situated sites within a 3-kb chromatin maintenance unit with a modular structure. Results of an in vivo analysis showed that these DNA fragments (each ∼400 bp) contain both TRX- and Polycomb-group response elements (TREs and PREs) and that in the context of the endogenousUltrabithorax gene, all of these elements are essential for proper maintenance of expression in embryos. Dissection of one of these maintenance modules showed that TRX- and Polycomb-group responsiveness is conferred by neighboring but separable DNA sequences, suggesting that independent protein complexes are formed at their respective response elements. Furthermore, we have found that the activity of this TRE requires a sequence (∼90 bp) which maps to within several tens of base pairs from the closest neighboring PRE and that the PRE activity in one of the elements may require a binding site for PHO, the protein product of the Polycomb-group genepleiohomeotic. Our results show that long-range maintenance of Ultrabithorax expression requires a complex element composed of cooperating modules, each capable of interacting with both positive and negative chromatin regulators.

Molecular genetic analysis of the Drosophila trithorax-related gene which encodes a novel SET domain protein.

The products of the trithorax and Polycomb groups genes maintain the activity and silence, respectively, of many developmental genes including genes of the homeotic complexes. This transcriptional regulation is likely to involve modification of chromatin structure. Here, we report the cloning and characterization of a new gene, trithorax-related (trr), which shares sequence similarities with members of both the trithorax and Polycomb groups. The trr transcript is 9.6 kb in length and is present throughout development. The TRR protein, as predicted from the nucleotide sequence of the open reading frame, is 2431 amino acids in length and contains a PHD finger-like domain and a SET domain, two highly conserved protein motifs found in several trithorax and Polycomb group proteins, and in modifiers of position effect variegation. TRR is most similar in sequence to the human ALR protein, suggesting that trr is a Drosophila homologue of the ALR. TRR is also highly homologous to Drosophila TRITHORAX protein and to its human homologue, ALL-1/HRX. However, preliminary genetic analysis of a trr null allele suggests that TRR protein may not be involved in regulation of homeotic genes (i.e. not a member of the trithorax or Polycomb groups) or in position effect variegation.

Runt domain partner proteins enhance DNA binding and transcriptional repression in cultured Drosophila cells

Background: The Drosophila gene runt plays multiple roles during embryogenesis, including one as a pair‐rule class segmentation gene. The runt protein (Runt) contains an evolutionarily conserved domain (the Runt domain) that is found in several mammalian proteins including the human protein AML1, which is involved in many chromosome translocations associated with leukaemia. Specific DNA binding activity of a mammalian Runt domain is enhanced by a partner protein called PEBP2β/CBFβ. DNA binding activity of Drosophila Runt is also stimulated by this protein, suggesting the existence of a similar Runt partner protein in Drosophila.

Conservation of structure and expression of the trithorax gene between Drosophila virilis and Drosophila melanogaster

The Drosophila melanogaster trithorax gene encodes several large RNAs which are expressed in complex patterns in the embryo. The D. virilis trithorax gene was isolated and sequenced. It produces a similar to D. melanogaster set of transcripts, and it encodes a protein that shows sequence similarity in several domains which are also conserved in human homologue, ALL-1/HRX. Previous experiments have suggested that a distinct expression domain of trithorax in the posterior region of the embryo is required to maintain expression of the BX-C genes (Sedkov et al., 1994, Development 120, 1907-1917). At cellular blastoderm, trithorax RNA expression in D. virilis embryos is also confined to the posterior portion of the presumptive mesoderm. This finding supports the idea that the specific BX-C-related expression domain is an essential feature of the trithorax gene.