Using a tobacco cDNA clone as a probe, a genomic clone coding for a tobacco ubiquitin extension protein was isolated. Nucleotide sequence determination of the clone identified an open reading frame for an ubiquitin unit of 76 amino acids and an extension tail of 80 amino acids. To the 5' upstream of the open reading frame, a sequence of 1,110 nucleotides was determined and a putative CCAAT box and TATA box were located. An intron sequence was not apparent as the open reading frame for the ubiquitin-extension protein was continuous for 468 nucleotides. In the 3' downstream region of the gene, a putative polyadenylation signal and GU rich region were observed. Northern blot analysis of tobacco transcripts with the tail part of the gene as a probe specifically identified the 1.3 kb transcript. The Northern signal at 1.3 kb indicated that the expression of the ubiquitin-extension protein gene in tobacco is downregulated upon heat-shock.
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