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 lambda-ZAP-cDNA library, generated from mRNA of tomato (Lycopersicon esculentum) cells grown in suspension for 3 days. The open reading frame called LeUBC1, encodes for a polypeptide with a predicted molecular mass of 21.37 kDa, which was confirmed by bacterial overexpression and SDS-PAGE, Database searches with LeUBC1 showed highest sequence similarities to UBC1 of bovine and yeast, By Southern blot analysis LeUBC1 was identified as a member of a small E2 subfamily of tomato, presumably consisting of at least two members. As revealed by Northern blot analysis LeUBC1 is constitutively expressed in an exponentially growing tomato cell culture. In response to heat shock an increase in LeUBC1-mRNA was detectable, A strong accumulation of the LeUBC1-transcript was observed by exposure to heavy metal stress which was performed by treatment with cadmium chloride (CdCl2). The cellular uptake of cadmium mas controlled via ICP-MS measurements, The data suggest that like in yeast, 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.