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 screening a cDNA library made from young cherry tomato fruit with a potato FK cDNA. The 1243 bp cDNA contains a 981 bp open reading frame encoding a 327 amino acid protein with a calculated molecular mass of 34 819 Da and an isoelectric point (pI) of 7.27. Southern-blot analysis suggests that in tomato, this FK is encoded by a single gene. The expression is controlled at the transcriptional level with mRNA primarily expressed in young fruit and mature root tissue. The FK protein is widely distributed in the plant except in leaf tissue. Enzyme activity is greatest 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 Science Ireland Ltd.