Meletzus D, Rudnick P, Doetsch N, Green A, Kennedy C
Department of Plant Pathology, College of Agriculture, University of Arizona, Tucson 85721, USA.
J Bacteriol. 1998 Jun;180(12):3260-4. doi: 10.1128/JB.180.12.3260-3264.1998.
To determine whether in Azotobacter vinelandii the PII protein influences the regulation of nif gene expression in response to fluxes in the ammonium supply, the gene encoding PII was isolated and characterized. Its deduced translation product was highly similar to PII proteins from other organisms, with the greatest degree of relatedness being exhibited to the Escherichia coli glnK gene product. A gene designated amtB was found downstream of and was contranscribed with glnK as in E. coli. The AmtB protein is similar to functionally characterized ammonium transport proteins from a few other eukaryotes and one other prokaryote. glnK and amtB comprise an operon. Attempts to isolate a stable glnK mutant strain were unsuccessful, suggesting that glnK, like glnA, is an essential gene in A. vinelandii. amtB mutants were isolated, and although growth on limiting amounts of ammonium was similar in the mutant and wild-type strains, the mutants were unable to transport [14C]methylammonium.
为了确定在棕色固氮菌中PII蛋白是否响应铵供应通量影响固氮基因表达的调控，编码PII的基因被分离并进行了表征。其推导的翻译产物与来自其他生物的PII蛋白高度相似，与大肠杆菌glnK基因产物的相关性最高。发现一个名为amtB的基因位于glnK下游，并且与glnK共转录，如同在大肠杆菌中一样。AmtB蛋白类似于来自其他一些真核生物和另一种原核生物的功能已得到表征的铵转运蛋白。glnK和amtB组成一个操纵子。分离稳定的glnK突变株的尝试未成功，这表明glnK与glnA一样，是棕色固氮菌中的一个必需基因。分离出了amtB突变体，尽管突变体和野生型菌株在有限量铵上的生长相似，但突变体无法转运[14C]甲基铵。
