(CT)n (GA)n repeats and heat shock elements have distinct roles in chromatin structure and transcriptional activation of the Drosophila hsp26 gene.

Abstract

Previous analysis of the hsp26 gene of Drosophila melanogaster has shown that in addition to the TATA box and the proximal and distal heat shock elements (HSEs) (centered at -59 and -340, relative to the start site of transcription), a segment of (CT),, repeats at -135 to -85 is required for full heat shock inducibility (R. L.Glaser, G. H. Thomas, E. S. Siegfried, S. C. R. Elgin, and J. T. Lis, J. Mol. Biol. 211:751-761, 1990). This (CT). element appears to contribute to formation of the wild-type chromatin structure of hsp26, an organized nucleosome array that leaves the HSEs in nucleosome-free, DNase I-hypersensitive (DH) sites (Q. Lu, L. L. Wallrath, B. D. Allan, R. L. Glaser, J. T. Lis, and S. C. R. Elgin, J. Mol. Biol. 225:985-998, 1992). Inspection of the sequences upstream of hsp26 has revealed an additional (CT). element at -347 to -341, adjacent to the distal HSE. We have analyzed the contribution of this distal (CT),, element (-347 to -341), the proximal (CT).element (-135 to -85), and the two HSEs both to the formation of the chromatin structure and to heat shock inducibility. hsp26 constructs containing site-directed mutations, deletions, substitutions, or rearrangements of these sequence elements have been fused in frame to the Escherichia coli lacZ gene and reintroduced into the D. melanogaster genome by P-element-mediated germ line transformation. Chromatin structure of the transgenes was analyzed (prior to gene activation) by DNase I or restriction enzyme treatment of isolated nuclei, and heat-inducible expression was monitored by measuring 13-galactosidase activity. The results indicate that mutations, deletions, or substitutions of either the distal or the proximal (CT), element affect the chromatin structure and heat-inducible expression of the transgenes. These (CT),, repeats are associated with a nonhistone protein(s) in vivo and are bound by a purified Drosophila protein, the GAGA factor, in vitro. In contrast, the HSEs are required for heat-inducible expression but play only a minor role in establishing the chromatin structure of the transgenes. Previous analysis indicates that prior to heat shock, these HSEs appear to be free of protein. Our results suggest that GAGA factor, an abundant protein factor required for normal expression of many Drosophila genes, and heat shock factor, a specific transcription factor activated upon heat shock, play distinct roles in gene regulation: the GAGA factor establishes and/or maintains the DH sites prior to heat shock induction, while the activated heat shock factor recognizes and binds HSEs located within the DH sites to trigger transcription.

Z-DNA-forming silencer in the first exon regulates human ADAM-12 gene expression

“…Z-DNA represents a higher energy state with a short half life unless it is stabilized by factors such as negative (−) DNA supercoiling, chemical modification, and proteins that can interact with Z-DNA (25)(26)(27)(28)(29). Expression of rat nucleolin gene (30), voltage-gated potassium channel Kv1.5 gene (31), human colony-stimulating factor 1(CSF-1) gene (32), hsp26 gene of Drosophila melanogaster (33), and macrophage immune response gene SLC11A1 (34) has been shown to be regulated by Z-DNA forming cis-acting elements. Z-DNA forming sequences have been shown to promote gene expression by acting as an enhancer of transcription (32,35) while in some cases they are shown to suppress gene expression (30,31,36).…”

Expression of the Arabidopsis HMG2 gene, encoding 3-hydroxy-3-methylglutaryl coenzyme A reductase, is restricted to meristematic and floral tissues.

“…However, there are two short polypyrimidine stretches (TCTCCTCCTTCTCTCC and TTCTTCTTCTTCTCCTCTCTC) located at position +49 and -113, respectively (Figure 2). d(CT), tracts in eukaryotic genomes may be involved in various processes, including replication (Baran et al, 1987;Caddle et al, 1990), recombination (Weinreb et al, 1990), transcription (Wells et al, 1988;Lu et al, 1993), and chromatin structure (Lu et al, 1993). Proteins that specifically bind (CT);(GA), promoter elements have been reported (Gilmour et al, 1989;Kolluri et al, 1992).…”

The fourth chromosome of Drosophila melanogaster : Interspersed euchromatic and heterochromatic domains

“…Chromatin structure was assessed by using XbaI digestion of nuclei from third-instar larvae as described (28,29). Purified DNA from XbaI-treated nuclei was digested to completion with SalI, run in a 1.2% agarose gel, transferred to a nylon membrane, and hybridized with the plant DNA fragment pt labeled with [␣-32 P]dATP and [␣-32 P]dCTP.…”