Sakakibara H, Takei K, Sugiyama T
Department of Applied Biological Sciences, Agricultural Sciences, Nagoya University, Japan.
Plant J. 1996 Nov;10(5):883-92. doi: 10.1046/j.1365-313x.1996.10050883.x.
A full-length cDNA clone, pZmSUMT1, encoding an S-adenosyl-L-methionine-dependent uroporphyrinogen III C-methyltransferase (SUMT; EC 2.1.1.107) of maize was isolated from a root cDNA library. pZmSUMT1 had an insert of 1.7 kb and the amino acid sequence deduced from the open reading frame of the cDNA was similar to that of SUMT from various bacteria and also to the SUMT catalytic region of siroheme synthase (cysG) from Escherichia coli. Overproduction of ZmSUMT1 in a cysG mutant of E. coli eliminated the requirement of the strain for cysteine. Transcripts for ZmSUMT1 accumulated rapidly in both rots and leaves in response to the addition of nitrate to the culture medium. The effects of biochemical inhibitors on the nitrate-dependent induction of the gene for ZmSUMT1 coincided with the effects on the genes for other nitrate-assimilatory enzymes, nitrate reductase and nitrite reductase. An import experiment in vitro suggested that the gene product might be located in plastids. The results together indicate that ZmSUMT1 might be involved in the synthesis of siroheme, a prosthetic group of nitrite reductase, and that the expression of its gene is co-regulated with that of other nitrate-assimilatory genes.
从玉米根cDNA文库中分离出一个全长cDNA克隆pZmSUMT1，它编码一种依赖S-腺苷-L-甲硫氨酸的尿卟啉原III C-甲基转移酶（SUMT；EC 2.1.1.107）。pZmSUMT1含有一个1.7 kb的插入片段，从该cDNA的开放阅读框推导的氨基酸序列与各种细菌的SUMT序列相似，也与大肠杆菌的siroheme合酶（cysG）的SUMT催化区域相似。在大肠杆菌的cysG突变体中过量表达ZmSUMT1消除了该菌株对半胱氨酸的需求。响应于向培养基中添加硝酸盐，ZmSUMT1的转录本在根和叶中均迅速积累。生化抑制剂对ZmSUMT1基因硝酸盐依赖性诱导的影响与对其他硝酸盐同化酶（硝酸还原酶和亚硝酸还原酶）基因的影响一致。体外导入实验表明该基因产物可能定位于质体中。这些结果共同表明ZmSUMT1可能参与亚硝酸还原酶辅基siroheme的合成，并且其基因表达与其他硝酸盐同化基因的表达共同调控。
