A putative nitrogenase reductase gene found in the nucleotide sequences from the photosynthetic gene cluster of R. capsulata.

Youvan et al . (Cell 37, 949-957,1984) recently reported the nucleotide and deduced polypeptide sequences of the photosynthetic reaction-center, B870 antenna, and flanking polypeptides from Rhodopseudomonas capsulata . The assignments of deduced peptide sequences of unknown function were based on the existence of open reading frames in the nucleotide sequences and on the identification of likely Shine-Dalgarno sequences preceding the open reading frames. Through a protein sequence homology search that compared the R . capsulata sequences to the protein sequence storage bank at the University of California, San Diego, we have identified an open reading frame similar in sequence to another protein in the sequence bank, namely, nitrogenase reductase . To maximize homology between the putative R . capsulata nitrogenase reductase and the corresponding enzymes of Anabaena (Mevarech et al ., PNAS 77, 6476-6480, 1980) and Clostridium (Tanaka et al ., J . Biol . Chem . 252, 7093-7100, 1977) it is necessary to alter the peptide assignments made in Figures 1, 3, and 4 of Youvan et al . (op . cit .) in the Bam HI-F fragment. The alteration required is the replacement of the F460 peptide with an F202 protein in the same reading frame as F460 and including all of the F460 protein . Thus, the new putative protein gene consists of the nucleotide sequence from F202 to F1020 . There is no obviously effective Shine-Dalgarno sequence preceding this putative gene . Furthermore, there is a 135 by overlap between F202 and F104, leaving a question whether both of these open reading frames are functionally significant . The alignments of the Anabaena and Clostridium nitrogenase reductase genes with the putative gene of