Le Brun N E, Bengtsson J, Hederstedt L
Department of Microbiology, Lund University, SE-223 62 Lund, Sweden.
Mol Microbiol. 2000 May;36(3):638-50. doi: 10.1046/j.1365-2958.2000.01883.x.
Cytochromes of c-type contain covalently bound haem and in bacteria are located on the periplasmic side of the cytoplasmic membrane. More than eight different gene products have been identified as being specifically required for the synthesis of cytochromes c in Gram-negative bacteria. Corresponding genes are not found in the genome sequences of Gram-positive bacteria. Using two random mutagenesis approaches, we have searched for cytochrome c biogenesis genes in the Gram-positive bacterium Bacillus subtilis. Three genes, resB, resC and ccdA, were identified. CcdA has been found previously and is required for a late step in cytochrome c synthesis and also plays a role in spore synthesis. No function has previously been assigned for ResB and ResC but these predicted membrane proteins show sequence similarity to proteins required for cytochrome c synthesis in chloroplasts. Attempts to inactivate resB and resC in B. subtilis have indicated that these genes are essential for growth. We demonstrate that various nonsense mutations in resB or resC can block synthesis of cytochromes c with no effect on other types of cytochromes and little effect on sporulation and growth. The results strongly support the recent proposal that Gram-positive bacteria, cyanobacteria, epsilon-proteobacteria, and chloroplasts have a similar type of machinery for cytochrome c synthesis (System II), which is very different from those of most Gram-negative bacteria (System I) and mitochondria (System III).
c型细胞色素含有共价结合的血红素，在细菌中位于细胞质膜的周质侧。已鉴定出超过八种不同的基因产物是革兰氏阴性菌中细胞色素c合成所特需的。在革兰氏阳性菌的基因组序列中未发现相应基因。我们采用两种随机诱变方法，在革兰氏阳性菌枯草芽孢杆菌中寻找细胞色素c生物合成基因。鉴定出了三个基因，resB、resC和ccdA。CcdA先前已被发现，是细胞色素c合成后期步骤所必需的，并且在孢子合成中也起作用。以前尚未确定ResB和ResC的功能，但这些预测的膜蛋白与叶绿体中细胞色素c合成所需的蛋白质具有序列相似性。在枯草芽孢杆菌中使resB和resC失活的尝试表明，这些基因对生长至关重要。我们证明，resB或resC中的各种无义突变可阻断细胞色素c的合成，而对其他类型的细胞色素无影响，对孢子形成和生长的影响也很小。结果有力地支持了最近的提议，即革兰氏阳性菌、蓝细菌、ε-变形菌和叶绿体具有类似类型的细胞色素c合成机制（系统II），这与大多数革兰氏阴性菌（系统I）和线粒体（系统III）的机制非常不同。
