The Bgl Ⅱ fragment carried in plasmid pMH903,which covers the nodD3 region of Rhizobium meliloti, has been sequenced. By using both S1 nuclease mapping and primer extension, two transcription start sites were demonst...The Bgl Ⅱ fragment carried in plasmid pMH903,which covers the nodD3 region of Rhizobium meliloti, has been sequenced. By using both S1 nuclease mapping and primer extension, two transcription start sites were demonstrated in the sequence. After the first transcription start site, there were two open reading frames (ORF) followed by the nodD3 coding sequence which was also preceded by the second promoter.The nodD3 gene under the first promoter mediated high,constitutive expression of nodC-lacZ fusion,and the gene under the second promoter required the product of nodD1 and alfalfa (Medicago sativa) seed exudate for the activation of fusion.Nodulation experiments showed that the nodD3 gene under either promoter was functional in eliciting nodules on alfalfa.The deletion of part of the two ORFs after the first promoter or deletion of the second promoter did not block the constitutive expression of nodC-lacZ fusion, whereas the deletion of the first promoter region or a polar insertion mutation between the two pr moters did cause nodD3 to activate nodC only in the presence of the inducer.It indicates that nodD3 can be transcribed from the first promoter as well as from a separate second promoter.展开更多
文摘欧洲环境卫星-高级合成孔径雷达(Environmental Satellite-Advanced Synthetic ApertureRadar,Envisat-ASAR)波模式数据提供了全球风、浪要素信息,在海浪模式预报与同化方面有重要作用。该数据合成孔径雷达(Synthetic Aperture Radar,SAR)图像普遍存在海浪条纹清晰度不同的现象,但是否影响数据精度尚无定论。本文通过比较2010年NODC(the National Oceanographic Date Center)浮标观测数据和波模式数据,发现经过官方修正后的海浪参数反而具有更大误差。进而通过对比不同条纹清晰度的SAR图像反演参数误差,揭示了ASAR产品海浪参数与浮标测量值之间的误差与海浪条纹清晰度的关系。结果表明:海浪条纹清晰的SAR图像的主波波长和主波周期的反演误差更小,而条纹不清晰SAR图像的有效波高和风速的反演误差更小。通过分析海浪参数对海浪条纹清晰度的敏感性,证实了有效波高和方位向截断波长对SAR图像条纹清晰度的响应最好,波陡次之,与卫星飞行方位角和入射角无关。因此,在反演和修正SAR波模式数据时,考虑图像的条纹清晰度,将会有效提高反演数据的精度。该研究可为高分三号等卫星的波模式数据波浪要素反演精度的提升提供有价值的参考。
基金Project supported by the National Natural Science Foundation of China.
文摘The Bgl Ⅱ fragment carried in plasmid pMH903,which covers the nodD3 region of Rhizobium meliloti, has been sequenced. By using both S1 nuclease mapping and primer extension, two transcription start sites were demonstrated in the sequence. After the first transcription start site, there were two open reading frames (ORF) followed by the nodD3 coding sequence which was also preceded by the second promoter.The nodD3 gene under the first promoter mediated high,constitutive expression of nodC-lacZ fusion,and the gene under the second promoter required the product of nodD1 and alfalfa (Medicago sativa) seed exudate for the activation of fusion.Nodulation experiments showed that the nodD3 gene under either promoter was functional in eliciting nodules on alfalfa.The deletion of part of the two ORFs after the first promoter or deletion of the second promoter did not block the constitutive expression of nodC-lacZ fusion, whereas the deletion of the first promoter region or a polar insertion mutation between the two pr moters did cause nodD3 to activate nodC only in the presence of the inducer.It indicates that nodD3 can be transcribed from the first promoter as well as from a separate second promoter.
