Summers M L, Meeks J C
Section of Microbiology, University of California, Davis 95616, USA.
Mol Microbiol. 1996 Nov;22(3):473-80. doi: 10.1046/j.1365-2958.1996.1371502.x.
The gene encoding glucose-6-phosphate dehydrogenase (G6PD), zwf, in Nostoc punctiforme strain ATCC 29133 is part of a four-gene operon that also encodes fructose bisphosphatase (fbp), transaldolase (tal) and a gene product termed OpcA, which is contranscribed with zwf and essential for G6PD activity. The effect of exogenous nitrogen and carbon sources on transcription of these genes was investigated. Growth in the presence of ammonium yielded low levels of transcripts encoding all genes of the operon, while growth under nitrogen-fixing conditions resulted in a large increase of transcripts encoding for fbp and zwf-opcA. When cells are grown in the presence of fructose, levels of transcripts encoding tal and zwf-opcA were increased, relative to levels in ammonium-grown cells. These results indicate that this facultatively heterotrophic cyanobacterium can respond to changes in its environment by altering transcription of genes involved in carbon catabolism. Primer extension identified five 5' ends corresponding to the major regulated transcripts which we conclude arise from independent transcriptional start points.
在点状念珠藻菌株ATCC 29133中，编码葡萄糖-6-磷酸脱氢酶（G6PD）的基因zwf是一个四基因操纵子的一部分，该操纵子还编码果糖双磷酸酶（fbp）、转醛醇酶（tal）以及一种名为OpcA的基因产物，OpcA与zwf共转录且对G6PD活性至关重要。研究了外源氮源和碳源对这些基因转录的影响。在铵存在的情况下生长时，编码操纵子所有基因的转录本水平较低，而在固氮条件下生长则导致编码fbp和zwf-opcA的转录本大幅增加。当细胞在果糖存在的情况下生长时，相对于在铵中生长的细胞，编码tal和zwf-opcA的转录本水平有所增加。这些结果表明，这种兼性异养蓝细菌可以通过改变参与碳分解代谢的基因转录来响应其环境变化。引物延伸鉴定出五个与主要调控转录本相对应的5'末端，我们得出结论，这些转录本源自独立的转录起始点。
