THE FUMR GENE ENCODING FUMARASE IN THE FILAMENTOUS FUNGUS RHIZOPUS-ORYZAE - CLONING, STRUCTURE AND EXPRESSION

The filamentous fungus Rhizopus oeyzae (Ro) is known for its ability t o overproduce and accumulate high levels of fumaric acid (FA) under st ress conditions. In order to study the molecular mechanisms involved i n the increased biosynthesis of FA, the gene (designated fumR) encodin g Ro fumarase was cloned and analysed for its structure and expression . Nucleotide (nt) sequence and comparison of the fumR product with fum arases from various sources established that fumR contains nine intron s and encodes a deduced product of 494 amino acids (aa), related to cl ass-II fumarases, A fumarase protein of 50 kDa was immune-detected in crude Ro extracts. Primer extension experiments mapped the 5' end of t he fumR RNA 159 nt upstream from the putative translation start codon. Both primer extension and Northern analysis showed the existence of o ne transcript of fumR. The level of fumR RNA increased in cells produc ing FA under stress conditions (high carbon and low nitrogen levels in the medium), suggesting that transcriptional regulation of fumR might be involved in the overproduction and accumulation of FA by Ro cells under stress conditions. The possibility that additional mechanisms ar e responsible for this phenomenon is discussed.