ISOLATION OF A CDNA CODING FOR AN UBIQUITIN-CONJUGATING ENZYME UBC1 OF TOMATO - THE FIRST STRESS-INDUCED UBC OF HIGHER-PLANTS

A clone of an ubiquitin-conjugating enzyme (UBC) was isolated from a l ambda-ZAP-cDNA library, generated from mRNA of tomato (Lycopersicon es culentum) cells grown in suspension for 3 days. The open reading frame called LeUBC1, encodes for a polypeptide with a predicted molecular m ass of 21.37 kDa, which was confirmed by bacterial overexpression and SDS-PAGE, Database searches with LeUBC1 showed highest sequence simila rities to UBC1 of bovine and yeast, By Southern blot analysis LeUBC1 w as identified as a member of a small E2 subfamily of tomato, presumabl y consisting of at least two members. As revealed by Northern blot ana lysis LeUBC1 is constitutively expressed in an exponentially growing t omato cell culture. In response to heat shock an increase in LeUBC1-mR NA was detectable, A strong accumulation of the LeUBC1-transcript was observed by exposure to heavy metal stress which was performed by trea tment with cadmium chloride (CdCl2). The cellular uptake of cadmium ma s controlled via ICP-MS measurements, The data suggest that like in ye ast, in plants a certain subfamily of UBC is specifically involved in the proteolytic degradation of abnormal proteins as result of stress. (C) 1997 Federation of European Biochemical Societies.