Shatters R G, Somerville J E, Kahn M L
Department of Microbiology, Washington State University, Pullman 99164-6340.
J Bacteriol. 1989 Sep;171(9):5087-94. doi: 10.1128/jb.171.9.5087-5094.1989.
Most rhizobia contain two glutamine synthetase (GS) enzymes: GSI, encoded by glnA, and GSII, encoded by glnII. We have found that WSU414, a Rhizobium meliloti 104A14 glutamine auxotroph derived from a glnA parental strain, is an ntrA mutant. The R. meliloti glnII promoter region contains DNA sequences similar to those found in front of other genes that require ntrA for their transcription. No GSII was found in the glnA ntrA mutant, and when a translational fusion of glnII to the Escherichia coli lacZ gene was introduced into WSU414, no beta-galactosidase was expressed. These results indicate that ntrA is required for glnII expression. The ntrA mutation did not prevent the expression of GSI. In free-living culture, the level of GSII and of the glnII-lacZ fusion protein was regulated by altering transcription in response to available nitrogen. No GSII protein was detected in alfalfa, pea, or soybean nodules when anti-GSII-specific antiserum was used.
大多数根瘤菌含有两种谷氨酰胺合成酶（GS）：由glnA编码的GSI和由glnII编码的GSII。我们发现，WSU414是一种源自glnA亲本菌株的苜蓿根瘤菌104A14谷氨酰胺营养缺陷型菌株，它是一种ntrA突变体。苜蓿根瘤菌glnII启动子区域包含的DNA序列，与其他需要ntrA进行转录的基因前的序列相似。在glnA ntrA突变体中未发现GSII，当将glnII与大肠杆菌lacZ基因的翻译融合体导入WSU414时，未表达β-半乳糖苷酶。这些结果表明，ntrA是glnII表达所必需的。ntrA突变并不妨碍GSI的表达。在自由生活培养中，GSII和glnII-lacZ融合蛋白的水平通过响应可用氮改变转录来调节。当使用抗GSII特异性抗血清时，在苜蓿、豌豆或大豆根瘤中未检测到GSII蛋白。
