Cloning and transcriptional analysis of the nifUHDK genes of Trichodesmium sp. IMS101 reveals stable nifD, nifDK and nifK transcripts
Cloning and transcriptional analysis of the nifUHDK genes of Trichodesmium sp. IMS101 reveals stable nifD, nifDK and nifK transcripts
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DOI：
10.1099/00221287-144-12-3359
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发表时间：
1998-12-01
期刊：
影响因子：
--
通讯作者：
Zehr, JP
中科院分区：
文献类型：
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作者：
Dominic, B;Chen, YB;Zehr, JP
毛霉(Trichodesum spp.)是能够好氧固氮的海洋丝状、非异质晶体蓝藻。本研究对毛霉菌的固氮酶结构基因(NifHDK)和nifU基因进行了研究。对IMS101进行克隆和测序。毛霉属(Trichodesmium sp.)IMS101的nifH、nifD和nifK氨基酸序列与鱼腥藻的同源性分别为79%、66%和68%。PCC7120菌株。在nifH起始密码子上游发现了一个潜在的nifH转录起始点212个碱基。在转录起始点上游发现了与鱼腥藻固氮酶基因非常相似的启动子类核苷酸序列。序列分析显示，在nifH和nifD下游的顺反子间区，DNA区域可能形成茎环结构。Northern杂交分析表明，存在与nifH、nifHD和nifHDK对应的转录本。令人惊讶的是，Northern杂交还发现了与nifD、nifDK和nifK对应的转录本的存在，这些转录本以前从未被报道为蓝藻连续的nifHDK基因的转录本。在硝酸盐浓度为20 mM或氧气浓度高达40%时，nifHDK基因的转录没有受到明显抑制，而氨和尿素则抑制了nifHDK的转录。NifHDK基因的转录不受黑暗的影响，这表明这些基因在毛霉中的转录不受光的直接调控。
Trichodesmium spp. are marine filamentous, non-heterocystous cyanobacteria capable of aerobic nitrogen fixation. In this study, the nitrogenase structural genes (nifHDK) and nifU gene of Trichodesmium sp. IMS101 were cloned and sequenced. The Trichodesmium sp. IMS101 nifH, nifD and nifK amino acid sequences showed only 79%, 66% and 68% identity, respectively, to those of Anabaena sp. strain PCC 7120. A potential transcription start site for nifH was found 212 bases upstream of the nifH start codon. Promoter-like nucleotide sequences upstream of the transcription start site were identified that were very similar to those identified for the nitrogenase genes of Anabaena spp. Sequence analysis revealed regions of DNA that may form stem-loop structures in the intercistronic regions downstream of nifH and nifD. RNA analysis by Northern hybridization revealed the presence of transcripts corresponding to nifH, nifHD and nifHDK. Surprisingly, Northern hybridization also revealed the presence of transcripts that corresponded to nifD, nifDK and nifK, which have not been previously reported as transcripts in contiguous nifHDK genes of cyanobacteria. Transcription of the nifHDK genes was not significantly repressed in the presence of nitrate at a final concentration of 20 mM or at oxygen concentrations of up to 40%, whereas ammonium and urea inhibited nifHDK transcription. The transcription of the nifHDK genes was not affected by darkness, which suggests that transcription of these genes in Trichodesmium is not directly regulated by light.