Witte Claus-Peter, Tiller Sarah, Isidore Edwige, Davies Howard V, Taylor Mark A
Scottish Crop Research Institute, Unit of Plant Biochemistry, Invergowrie, Dundee DD2 5DA, UK.
J Exp Bot. 2005 Jan;56(409):91-9. doi: 10.1093/jxb/eri014. Epub 2004 Nov 8.
Globally, urea is the most widely used nitrogen fertilizer and is made accessible to plants via the urease reaction. However, sequence information for the plant enzyme is scarce. A cDNA encoding urease from soybean (Glycine max) has been cloned and sequence information has been obtained for two alleles (11 and 19 kbp, respectively) of the potato (Solanum tuberosum, cv. Desiree) urease gene and the corresponding cDNAs. It was found that urease is encoded by a single copy gene in several solanaceous species, and maps to chromosome V in potato. By contrast, the presence of two urease genes was reported for soybean. Comparative analysis of 11 kbp overlapping allelic DNA allowed the quantification of single nucleotide polymorphisms and revealed the presence of a truncated Ty1-copia retrotransposon in one of the alleles. Both alleles contained a copy of a terminal-repeat retrotransposon in miniature (TRIM). 25-50% of urease pre-mRNAs from both alleles were alternatively spliced in a variety of different ways. The retrotransposons had no effect on splicing. While urease is expressed in all tissues tested, its mRNA and protein are of low abundance. The TATA-less urease promoter appears to drive low-level housekeeping transcription. An in silico analysis showed that eukaryotic urease protein sequences are very similar to sequences from prokaryotic enzymes, conserving all residues of known functional importance. It is therefore likely that all known ureases are structurally similar, employing the same catalytic mechanism.
在全球范围内，尿素是使用最广泛的氮肥，可通过脲酶反应供植物利用。然而，关于植物脲酶的序列信息却很少。已克隆出编码大豆（Glycine max）脲酶的cDNA，并获得了马铃薯（Solanum tuberosum，品种Desiree）脲酶基因的两个等位基因（分别为11和19 kbp）及其相应cDNA的序列信息。研究发现，脲酶在几种茄科植物中由单拷贝基因编码，并定位于马铃薯的第五条染色体上。相比之下，据报道大豆存在两个脲酶基因。对11 kbp重叠等位基因DNA的比较分析能够对单核苷酸多态性进行定量，并揭示其中一个等位基因中存在一个截短的Ty1-copia逆转座子。两个等位基因均含有一个微型末端重复逆转座子（TRIM）的拷贝。两个等位基因中25 - 50%的脲酶前体mRNA以多种不同方式进行可变剪接。逆转座子对剪接没有影响。虽然脲酶在所有测试组织中均有表达，但其mRNA和蛋白质丰度较低。无TATA框的脲酶启动子似乎驱动低水平的持家转录。计算机分析表明，真核脲酶蛋白序列与原核酶的序列非常相似，保留了所有已知功能重要性的残基。因此，所有已知的脲酶在结构上可能相似，采用相同的催化机制。
