3 CLASSES OF THE HEAT-SHOCK RESPONSE OF THE UBIQUITIN GENE FAMILY IN NICOTIANA-TABACUM

We have isolated a tobacco ubiquitin cDNA clone, pTUQC-1 which encodes two full-length, almost identical 76-amino acid repeats, in a polypro tein conformation. The deduced amino acid sequence of the mature monom eric polypeptide is very similar to that determined for Arabidopsis, e xcept for four amino acids. Genomic DNA blot analysis using pTUQC-1 as a probe revealed that ubiquitin is encoded by a small multigene famil y in tobacco, broccoli and tomatoes. RNA blot analysis indicated that multiple ubiquitin mRNAs of 1.3, 1.9 and 2.6 kb are produced in tobacc o. The two larger transcripts were expressed transiently between 30 mi n and 1 h after heat-shock at 43 degrees C, then decreased dramaticall y within 2 h. The expression was not detected at higher heat-shock tem peratures. In contrast, the 1.3 kb did not appear upon heat-shock Blot analysis of RNA extracted from the leaves at various developmental st ages of tobacco indicated that 1.3 and 1.9 kb transcripts were constit utively expressed at a low level.