A cDNA encoding a putative SPF1-type DNA-binding protein from cucumber

A cDNA clone encoding a polypeptide with homology to the novel SPF1 DNA-binding protein of sweet potato has been isolated from a cDNA library from RNA of senescing cucumber (Cucumis sativus, L.) cotyledons. Comparison of the two sequences reveals similar features which may be important in the evolution and function of this protein, including a duplicated region of about 56 amino acids (aa). The first half of the duplicated region is enriched in basic aa and is very highly conserved, both within and between each polypeptide. In contrast, the second half of the duplicated region is poorly conserved within each polypeptide, but highly conserved when cucumber and sweet potato sequences are compared. Southern blot analysis with cucumber DNA shows a simple hybridisation 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 senescence. The possibility that the cucumber SPF1-type protein may be involved in carbohydrate regulation of gene expression is discussed.