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Journal of Bacteriology, May 2004, p. 3143-3152, Vol. 186, No. 10
0021-9193/04/$08.00+0     DOI: 10.1128/JB.186.10.3143-3152.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.

Involvement of the C-Terminal Extension of the Polypeptide and of the PucC Protein in LH2 Complex Biosynthesis in Rubrivivax gelatinosus

Anne-Soisig Steunou, Soufian Ouchane, Françoise Reiss-Husson, and Chantal Astier^*

Centre de Génétique Moléculaire du Centre National de la Recherche Scientifique (UPR 2167), 91198 Gif sur Yvette CEDEX, France

Received 5 November 2003/ Accepted 23 January 2004

The facultative phototrophic nonsulfur bacterium Rubrivivax gelatinosus exhibits several differences from other species of purple bacteria in the organization of its photosynthetic genes. In particular, the puc operon contains only the pucB and pucA genes encoding the ß and polypeptides of the light-harvesting 2 (LH2) complex. Downstream of the pucBA operon is the pucC gene in the opposite transcriptional orientation. The transcription of pucBA and pucC has been studied. No pucC transcript was detected either by Northern blotting or by reverse transcription-PCR analysis. The initiation site of pucBA transcription was determined by primer extension, and Northern blot analysis revealed the presence of two transcripts of 0.8 and 0.65 kb. The half-lives of both transcripts are longer in cells grown semiaerobically than in photosynthetically grown cells, and the small transcript is the less stable. It was reported that the polypeptide, encoded by the pucA gene, presents a C-terminal extension which is not essential for LH2 function in vitro. The biological role of this alanine- and proline-rich C-terminal extension in vivo has been investigated. Two mutants with C-terminal deletions of 13 and 18 residues have been constructed. Both present the two pucBA transcripts, while their phenotypes are, respectively, LH2⁺ and LH2^–, suggesting that a minimal length of the C-terminal extension is required for LH2 biogenesis. Another important factor involved in the LH2 biogenesis is the PucC protein. To gain insight into the function of this protein in R. gelatinosus, we constructed and characterized a PucC mutant. The mutant is devoid of LH2 complex under semiaerobiosis but still produces a small amount of these antennae under photosynthetic growth conditions. This conditional phenotype suggests the involvement of another factor in LH2 biogenesis.

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* Corresponding author. Mailing address: Centre de Génétique Moléculaire du Centre National de la Recherche Scientifique (UPR 2167), BÂt. 26, Ave. de la Terrasse, 91198 Gif sur Yvette CEDEX, France. Phone: 33-1-69823137. Fax: 33-1-69823230. E-mail: astier{at}cgm.cnrs-gif.fr.

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Journal of Bacteriology, May 2004, p. 3143-3152, Vol. 186, No. 10
0021-9193/04/$08.00+0     DOI: 10.1128/JB.186.10.3143-3152.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.

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