SEQUENCE-ANALYSIS OF PRE-FERREDOXIN-NADP-REDUCTASE CDNA FROM CYANOPHORA-PARADOXA SPECIFYING A PRECURSOR FOR A NUCLEUS-ENCODED CYANELLE POLYPEPTIDE()

A cDNA clone for pre-ferredoxin-NADP+ reductase (FNR) was obtained by screening a Cyanophora paradoxa expression library with antibodies spe cific for cyanelle FNR. The 1.4 kb transcript was derived from a singl e-copy gene. The precursor (41 kDa) and mature forms (34 kDa) of FNR w ere identified by western blotting of in vitro translation products an d cyanelle extracts, respectively. The derived amino acid sequence of the mature form was corroborated by data from N-terminal protein seque ncing and yielded identity scores from 58% to 62% upon comparison with cyanobacterial FNRs. Sequence conservation seemed to be even more pro nounced in comparison with enzymes from higher plants, but using the n eighbor joining method the C. paradoxa sequence was clearly positioned between the prokaryotic and eukaryotic sequences. The transit peptide of 65 or 66 amino acids appeared to be totally unrelated to those fro m spinach, pea and ice plant but showed overall characteristics of str oma-targeting peptides.