Schlösser T, Schmidt G, Stahmann K P
Institut für Biotechnologie 1, Forschungszentrum Jülich GmbH, D-52425 Jülich, Germany.
Microbiology (Reading). 2001 Dec;147(Pt 12):3377-86. doi: 10.1099/00221287-147-12-3377.
The filamentous hemiascomycete Ashbya gossypii is a strong riboflavin overproducer. A striking but as yet uninvestigated phenomenon is the fact that the overproduction of this vitamin starts when growth rate declines, which means that most of the riboflavin is produced in the stationary phase, the so-called production phase. The specific activity of 3,4-dihydroxy-2-butanone 4-phosphate (DHBP) synthase, the first enzyme in the biosynthetic pathway for riboflavin, was determined during cultivation and an increase during the production phase was found. Furthermore, an increase of RIB3 mRNA, encoding DHBP synthase, was observed by competitive RT-PCR in the production phase. The mRNAs of two housekeeping genes, ACT1 (encoding actin) and TEF (encoding translation elongation factor-1 alpha), served as standards in the RT-PCR. Reporter studies with a RIB3 promoter-lacZ fusion showed an increase of beta-galactosidase specific activity in the production phase. This investigation verified that the increase of RIB3 mRNA in the production phase is caused by an induction of promoter activity. These data suggest that the time course of riboflavin overproduction of A. gossypii is correlated with a transcriptional regulation of the DHBP synthase.
丝状半子囊菌棉阿舒囊霉是一种强力核黄素过量生产者。一个引人关注但尚未得到研究的现象是，这种维生素的过量生产始于生长速率下降之时，这意味着大部分核黄素是在稳定期（即所谓的生产阶段）产生的。在培养过程中测定了核黄素生物合成途径中的首个酶——3,4-二羟基-2-丁酮4-磷酸（DHBP）合酶的比活性，发现在生产阶段其活性有所增加。此外，通过竞争性逆转录聚合酶链反应（RT-PCR）观察到，在生产阶段编码DHBP合酶的RIB3 mRNA有所增加。在RT-PCR中，两个持家基因ACT1（编码肌动蛋白）和TEF（编码翻译延伸因子-1α）的mRNA用作标准对照。用RIB3启动子 - lacZ融合进行的报告基因研究表明，在生产阶段β-半乳糖苷酶比活性有所增加。这项研究证实，生产阶段RIB3 mRNA的增加是由启动子活性的诱导所致。这些数据表明，棉阿舒囊霉核黄素过量生产的时间进程与DHBP合酶的转录调控相关。
