The pucC genes of Rubrivivax gelatinosus strain 151 and Rhodopseudomonas acidophila strain 10050 have been identified, cloned and sequenced. In Rubrivivax gelatinosus the arrangement of the pucC gene with regard to the pucBA genes was shown to differ from that found in other species of photosynthetic bacteria. The Rhodopseudomonas acidophila pucC was found downstream of four new pucBA gene pairs, bringing the sequenced pucBA pairs to a total of eight in this strain. The predicted PucC protein sequences were compared to those of PucC from other species and showed high similarity. Similarity was also seen to more distantly related proteins LhaA and orf428 of Rhodobacter capsulatus, orf G115 of Rhodospirillum rubrum and 'orf428' from Synechocystis sp. PCC6803. An analysis of the predicted secondary structure of these proteins is given, and their structural similarity to proteins in the Major Facilitator Superfamily is discussed with regard to their possible function.