Nucleotide and amino acid sequence of a Cucurbita phytochrome cDNA clone: identification of conserved features by comparison with Avena phytochrome.

The amino acid (aa) sequence of Cucurbita phytochrome has been deduced from the nucleotide (nt) sequence of a cDNA clone which was initially identified by hybridization to an Avena phytochrome cDNA clone. Cucurbita, a dicot, and Avena, a monocot, represent evolutionarily divergent groups of plants. The Cucurbita phytochrome polypeptide is 1123 aa in length, corresponding to 125 kDa. Overall, the Cucurbita and Avena phytochrome sequences are 65% homologous at both the nt and aa levels but this sequence conservation is not evenly distributed. Most of the N-terminal two-thirds of the aligned polypeptide chains exhibits localized regions of high conservation, while the extreme N terminus and the C-terminal one-third are less homologous. Comparison of the predicted hydropathic properties of these polypeptides also indicates conservation of domains of phytochrome structure. The possible correlation of these conserved structural features with previously identified functional domains of phytochrome is discussed.