Jenkins L S, Nunn W D
J Bacteriol. 1987 May;169(5):2096-102. doi: 10.1128/jb.169.5.2096-2102.1987.
The expression of the Ato enzymes, acetyl coenzyme A:acetoacetyl coenzyme A transferase and thiolase II, is required for growth of Escherichia coli on short-chain fatty acids. The structural genes for these enzymes, atoD, atoA, and atoB, respectively, make up the ato operon. A 48-kilodalton protein encoded by atoC was required for the synthesis or activation of the Ato enzymes. The expression of Ato enzyme activities was inducible in atoC+ strains, constitutive in atoCc strains, and noninducible in atoC mutants. Merodiploid studies demonstrated that the atoCc allele is trans-dominant to the atoC+ allele. To study the action of the trans-acting atoC-encoded activator, the promoter of the ato operon was fused to the promoterless galK gene and introduced into a low-copy-number vector. The resulting low-copy-number fusion plasmid was introduced into atoC+, atoC, and atoCc hosts. The expression of the fused galK gene was inducible in the atoC+ host, noninducible in atoC host strains, and constitutive when harbored in the atoCc host. This indicated that the atoC+ and atoCc gene products act at the level of transcription, stimulating the expression of the ato operon. A working model consistent with these results is presented.
大肠杆菌在短链脂肪酸上生长需要乙酰辅酶A：乙酰乙酰辅酶A转移酶（Ato酶）和硫解酶II的表达。这些酶的结构基因分别为atoD、atoA和atoB，它们共同构成了ato操纵子。atoC编码的一种48千道尔顿的蛋白质是合成或激活Ato酶所必需的。在atoC⁺菌株中，Ato酶活性的表达是可诱导的；在atoCc菌株中是组成型的；而在atoC突变体中是不可诱导的。部分二倍体研究表明，atoCc等位基因对atoC⁺等位基因是反式显性的。为了研究由atoC编码的反式作用激活剂的作用，将ato操纵子的启动子与无启动子的galK基因融合，并导入低拷贝数载体。将得到的低拷贝数融合质粒导入atoC⁺、atoC和atoCc宿主中。融合的galK基因的表达在atoC⁺宿主中是可诱导的，在atoC宿主菌株中是不可诱导的，而当存在于atoCc宿主中时是组成型的。这表明atoC⁺和atoCc基因产物在转录水平起作用，刺激ato操纵子的表达。本文提出了一个与这些结果一致的工作模型。
