A CDNA-ENCODING A PUTATIVE SPF1-TYPE DNA-BINDING PROTEIN FROM CUCUMBER

A cDNA clone encoding a polypeptide with homology to the novel SPF1 DN A-binding protein of sweet potato has been isolated from a cDNA librar y from RNA of senescing cucumber (Cucumis sativus, L.) cotyledons. Com parison of the two sequences reveals similar features which may be imp ortant in the evolution and function of this protein, including a dupl icated region of about 56 amino acids (aa). The first half of the dupl icated region is enriched in basic aa and is very highly conserved, bo th within and between each polypeptide. In contrast, the second half o f the duplicated region is poorly conserved within each polypeptide, b ut highly conserved when cucumber and sweet potato sequences are compa red. Southern blot analysis with cucumber DNA shows a simple hybridisa tion pattern indicating one or very few genes. Northern blot analysis shows that the expression of the cucumber gene increases in cotyledons as they expand and become photosynthetic and remains high in senescen ce. The possibility that the cucumber SPF1-type protein may be involve d in carbohydrate regulation of gene expression is discussed.