Ferredoxin:NADP oxidoreductase of Cyanophora paradoxa: purification, partial characterization, and N-terminal amino acid sequence

Codon usage adaptation in the ferredoxin-NADP+ oxidoreductase of Cyanophora paradoxa upon translocation from cyanoplast to nucleus

Previous investigations of the petH gene of the biflagellated autotrophic protist Cyanophora paradoxa (Cp; Glaucocystophyta), descendant of an original endocyanome (symbiotic consortium of a eukaryote with an endocytobiotic cyanobacterium), established that: (i) the gene coding for a cyanoplast protein (FNR) is located on the nuclear genome; (ii) the sequence of the mature protein shows a high degree of amino-acid conservation to cyanobacterial homologs; (iii) the sequence of the transit peptide of the pre-protein displays poor, if any, homology to counterparts in higher plants. Here, we show that the G+C content and codon usage of this gene are most similar to a genuine nuclear gene. By contrast, the G+C content and codon usage display substantial differences to a collection of 30 cyanoplast encoded genes mainly attributable to alterations in the third codon position. Correspondence analysis on codon preference parameters corroborates the claim of codon usage adaptation of the translocated gene to the nuclear pattern. As a consequence, codon usage distances of genes of Cp encoded either by the nucleus or the cyanoplasts vs. homologous genes of the cyanobacterium, Anabaena, are notably different; this result has important phylogenetic implications.

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 specific for cyanelle FNR. The 1.4 kb transcript was derived from a single-copy gene. The precursor (41 kDa) and mature forms (34 kDa) of FNR were identified by western blotting of in vitro translation products and cyanelle extracts, respectively. The derived amino acid sequence of the mature form was corroborated by data from N-terminal protein sequencing and yielded identity scores from 58% to 62% upon comparison with cyanobacterial FNRs. Sequence conservation seemed to be even more pronounced in comparison with enzymes from higher plants, but using the neighbor 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 from spinach, pea and ice plant but showed overall characteristics of stroma-targeting peptides.