Bollivar D W, Suzuki J Y, Beatty J T, Dobrowolski J M, Bauer C E
Department of Biology, Indiana University Bloomington 47405.
J Mol Biol. 1994 Apr 15;237(5):622-40. doi: 10.1006/jmbi.1994.1260.
Previous studies have established that most if not all of the genes required for synthesis of the Rhodobacter capsulatus essential photosystem are clustered on a 46 kb region of the chromosome known as the photosynthesis gene cluster. This region has recently been sequenced in its entirety by Hearst and co-workers, revealing the existence of 23 open reading frames, many of which are thought to be involved in the synthesis of bacteriochlorophyll. In this study we have undertaken a systematic directed mutational analysis of 12 open reading frames in the photosynthesis gene cluster to evaluate whether individual open reading frames have a role in photopigment biosynthesis. The results of this analysis demonstrate that mutations constructed in seven open reading frames resulted in a loss of bacteriochlorophyll biosynthesis, concomitant with the accumulation of specific intermediates in the Mg-tetrapyrrole biosynthetic pathway. One mutation was observed to result in partial disruption of bacteriochlorophyll biosynthesis, leading to the accumulation of bacteriochlorophyll as well as an intermediate in the biosynthetic pathway. We also observed that disruptions constructed in four open reading frames had no discernible effect on the synthesis of photopigments. The results of this analysis are discussed with regard to our current understanding of the role of each of these open reading frames in the synthesis of the R. capsulatus photosystem.
以往的研究表明，合成荚膜红细菌必需光系统所需的大多数（如果不是全部）基因都聚集在染色体上一个46 kb的区域，即光合作用基因簇。赫斯特及其同事最近对该区域进行了全序列测定，发现了23个开放阅读框，其中许多被认为参与细菌叶绿素的合成。在本研究中，我们对光合作用基因簇中的12个开放阅读框进行了系统的定向突变分析，以评估单个开放阅读框在光合色素生物合成中是否起作用。该分析结果表明，在7个开放阅读框中构建的突变导致细菌叶绿素生物合成丧失，同时在镁四吡咯生物合成途径中积累特定中间体。观察到一个突变导致细菌叶绿素生物合成部分中断，导致细菌叶绿素以及生物合成途径中的一种中间体积累。我们还观察到，在4个开放阅读框中构建的破坏对光合色素的合成没有明显影响。结合我们目前对这些开放阅读框在荚膜红细菌光系统合成中各自作用的理解，对该分析结果进行了讨论。
