Puffing with PARP

摘要

Environmental stimuli such as heat shock, hormone treatment, stress, or acute infection induce the transcription of certain target genes. The tran-scriptional response is rapid, producing many mRNA transcripts, but transient, fading shortly after the inducing signal disappears. In the fruit fly Drosophila, this rapid transcriptional response is clearly visible under the microscope as "puffs" in the giant polytene chromosomes of the salivary glands. (These giant chromosomes are produced by repeated cycles of DNA replication in the absence of cell division.) Within minutes of a heat shock stimulus, the chromosomal sites of heat shock genes become decondensed, swell to many times their original diameter, and accumulate many new mRNA transcripts. Similar puffs occur at chromosomal sites of hormone-responsive genes in response to increased production of the steroid hormone ecdysone in Drosophila larvae approaching pupation.