Blume A J, Weber A, Balbinder E
J Bacteriol. 1968 Jun;95(6):2230-41. doi: 10.1128/jb.95.6.2230-2241.1968.
A comparison of the rates of synthesis of the tryptophan biosynthetic enzymes of Salmonella typhimurium under derepression showed that the genes of the trp operon can be expressed in a coordinate fashion in auxotrophs carrying nonpolar mutations. This coordination disappeared in trpA polar mutants. The loss of coordination affected only trpB, the second gene in the operon, which was always more drastically affected than the three distal genes. Polar mutations in trpA, the first gene of the trp operon, reduced the rates of synthesis of the tryptophan biosynthetic enzymes under conditions of derepression. When these rates were measured and correlated with the map position of each polar mutation, a polarity gradient of decreasing intensity (moving distally from the operator end of the gene) was obtained. Certain mutations ("unusual mutations") mapping at the operator distal end of trpA, and considered by other workers to correspond to the operator proximal end of trpB, were found to be polar. The bearing of our observations on the question of coordinate versus semicoordinate expression of the trp genes and the status of the "unusual mutations" is discussed.
对鼠伤寒沙门氏菌色氨酸生物合成酶在去阻遏状态下的合成速率进行比较，结果表明，在携带非极性突变的营养缺陷型菌株中，色氨酸操纵子的基因能够以协同的方式表达。这种协同性在trpA极性突变体中消失了。协同性的丧失仅影响到操纵子中的第二个基因trpB，它受到的影响总是比三个远端基因更为严重。色氨酸操纵子的第一个基因trpA中的极性突变，降低了去阻遏状态下色氨酸生物合成酶的合成速率。当测量这些速率并将其与每个极性突变的图谱位置相关联时，得到了一个强度递减的极性梯度（从基因的操纵子末端向远端移动）。某些位于trpA操纵子远端的突变（“异常突变”），其他研究者认为它们对应于trpB操纵子近端，被发现具有极性。本文讨论了我们的观察结果对于色氨酸基因协同表达与半协同表达问题以及“异常突变”状态的意义。
