The nucleus-limited Hsr-omega-n transcript is a polyadenylated RNA with a regulated intranuclear turnover.
The Drosophila Hsr-omega puff, one of the largest heat shock puffs, reveals a very unusual gene, identified by heat shock but constitutively active in nearly all cell types. Surprisingly, Hsr-omega yields two transcription end-products with very different roles. The larger, omega-n, is a nuclear RNA with characteristics suggesting a new class of nuclear RNAs. Although it neither leaves the nucleus nor undergoes processing, omega-n RNA is polyadenylated, showing that polyadenylation is not limited to cytoplasmic RNA, but possibly has a function in the nucleus. The amount of omega-n within the nucleus is specifically regulated by both transcription and turnover. Heat shock and several other agents cause rapid increases in omega-n. A rapid return to constitutive levels follows withdrawal of the agents. Degradation of omega-n is inhibited by actinomycin D, suggesting a novel intranuclear mechanism for RNA turnover. Within the nucleus, some omega-n RNA is concentrated at the transcription site; however, most is evenly distributed over the nucleus, showing no evidence of a concentration gradient which might be produced by simple diffusion from the site of transcription. Previous studies suggested that omega-n has a novel regulatory role in the nucleus. The actinomycin D-sensitive degradation system makes possible rapid changes in the amount of omega-n, allowing the putative regulatory activities to reflect cellular conditions at a given time. Omega-n differs from the best studied nuclear RNAs, snRNAs, in many ways. Omega-n demonstrates the existence of intranuclear mechanisms for RNA turnover and localization that may be used by a new class of nuclear RNAs.
Hogan
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NC
Department of Biology, Massachusetts Institute of Technology, Cambridge 02139.
Traverse
K L
KL
Sullivan
D E
DE
Pardue
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ML
D000818:Animals; D001483:Base Sequence; D002460:Cell Line; D002467:Cell Nucleus / Q000378:metabolism; D003609:Dactinomycin / Q000494:pharmacology; D004331:Drosophila melanogaster / Q000235:genetics*; D005786:Gene Expression Regulation / Q000187:drug effects; D017344:Genes, Insect; D006358:Hot Temperature; D008969:Molecular Sequence Data; D011061:Poly A / Q000378:metabolism; D012313:RNA / Q000378:metabolism*; D012323:RNA Processing, Post-Transcriptional; D012091:Repetitive Sequences, Nucleic Acid; D014158:Transcription, Genetic
D003609:Dactinomycin; D011061:Poly A; D012313:RNA