CdsA is a CDP-diacylglycerol synthase essential for phospholipid and glycolipid MPIase biosynthesis, and therefore for growth. The initiation codon of CdsA has been assigned as “TTG,” while methionine at the 37th codon was reported to be an initiation codon in the original report. Since a vector containing the open reading frame starting with “TTG” under a controllable promoter complemented the cdsA knockout, “TTG” could function as an initiation codon. However, no evidence supporting that this “TTG” is the sole initiation codon has been reported. We determined the initiation codon by examining the ability of mutants around the N-terminal region to complement cdsA mutants. Even if the “TTG” was substituted with a stop codon, the clear complementation was observed. Moreover, the clones with multiple mutations of stop codons complemented the cdsA mutant up to the 37th codon, indicating that cdsA possesses multiple codons that can function as initiation codons. We constructed an experimental system in which the chromosomal expression of cdsA can be analyzed. By means of this system, we found that the cdsA mutant with substitution of “TTG” with a stop codon is fully functional. Thus, we concluded that CdsA contains multiple initiation codons.

中文翻译：

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CdsA 是一种参与磷脂和糖脂 MPIase 生物合成的 CDP-二酰基甘油合酶，拥有多个起始密码子

CdsA 是一种 CDP-二酰基甘油合酶，对于磷脂和糖脂 MPIase 生物合成以及生长至关重要。 CdsA 的起始密码子被指定为“TTG”，而第 37 个密码子的甲硫氨酸被报道为原始报告中的起始密码子。由于在可控启动子下含有以“TTG”开头的开放阅读框的载体与cdsA敲除互补，因此“TTG”可以充当起始密码子。然而，没有证据表明该“TTG”是唯一的起始密码子。我们通过检查 N 末端区域周围的突变体补充cdsA突变体的能力来确定起始密码子。即使“TTG”被终止密码子取代，也观察到明显的互补。此外，具有多个终止密码子突变的克隆与cdsA突变体互补至第37个密码子，表明cdsA拥有多个可以充当起始密码子的密码子。我们构建了一个可以分析cdsA染色体表达的实验系统。通过该系统，我们发现用终止密码子替换“TTG”的cdsA突变体具有完全功能。因此，我们得出结论，CdsA含有多个起始密码子。