MOLECULAR-CLONING AND ANALYSIS OF FRUCTOKINASE EXPRESSION IN TOMATO (LYCOPERSICON-ESCULENTUM MILL)

A cDNA encoding a tomato (Lycopersicon esculentum Mill.) fructokinase (FK, ATP:fructose-6-phosphotransferase, E.C. 2.7.1.4) was cloned by sc reening a cDNA library made from young cherry tomato fruit with a pota to FK cDNA. The 1243 bp cDNA contains a 981 bp open reading frame enco ding a 327 amino acid protein with a calculated molecular mass of 34 8 19 Da and an isoelectric point (pI) of 7.27. Southern-blot analysis su ggests that in tomato, this FK is encoded by a single gene. The expres sion is controlled at the transcriptional level with mRNA primarily ex pressed in young fruit and mature root tissue. The FK protein is widel y distributed in the plant except in leaf tissue. Enzyme activity is g reatest in the developing fruits, but substantial activity is present in mature petioles and stems too. Protein and/or mRNA stability may be a factor in determining enzyme activity levels, however, differential expression of multiple genes may also explain differences between FK protein/FK activity levels and FK mRNA levels. (C) 1997 Elsevier Scien ce Ireland Ltd.