PRIMARY STRUCTURE, DEDUCED FROM CDNA, SECONDARY STRUCTURE-ANALYSIS AND CONCLUSIONS CONCERNING INTERACTION SURFACES OF THE DELTA-SUBUNIT OF THE PHOTOSYNTHETIC ATP-SYNTHASE (EC 3.6.1.34) FROM MILLET (SORGHUM-BICOLOR) AND MAIZE (ZEA-MAYS)

Lambdagt11 cDNA clones for the nuclear-encoded subunit delta of the ch loroplast ATP-synthase from Zea mays and Sorghum bicolor were sequence d. The processing site for S. bicolor delta was established, and the s equence of the mature subunit delta from Z. mays was completed by N-te rminal sequencing of the proteins isolated from chloroplasts. Only fiv e amino acids are identical and not more than 16% conservatively excha nged in all sequences of delta subunits from higher plants and the cor responding proteins from alga, bacteria and mitochondria (OSCP) availa ble. In binary comparison the comparatively high conservation of hydro philic residues indicates the importance of the surface of delta. The degree in identities of surface residues correlates with the capacity in hybrid reconstitution of photophosphorylation. A hypothetical secon dary structure model for a typical delta subunit can be deduced from p rediction algorithms. Three putative amphipathic alpha helices and an antiparallel amphipathic beta sheet seem to be conserved. These common secondary structure features should be significant for the function o f the delta subunit of F0F1 ATPases.