Pawlowski K, Twigg P, Dobritsa S, Guan C, Mullin B C
Department of Molecular Biology, Agricultural University, Wageningen, The Netherlands.
Mol Plant Microbe Interact. 1997 Jul;10(5):656-64. doi: 10.1094/MPMI.1997.10.5.656.
Two cDNAs representing different members (agNt84 and ag164) of a gene family encoding glycine- and histidine-rich proteins have been isolated from cDNA libraries from Alnus glutinosa root nodules. Expression of the corresponding genes could only be detected in nodules. With in situ hybridization, the expression in nodules was found to occur in young, infected cells of the prefixation zone (zone 2). The encoded proteins contain putative signal peptides for targeting to the endomembrane system, sharing sequence similarity with signal peptides from plant glycine-rich proteins, among them nodulin 24, a nodule-specific protein from soybean. This similarity suggests that, analogous to nodulin-24, proteins encoded by agNt84/ag164 may be located at the interface between the host plant membrane and the matrix surrounding the endosymbiont. The 3' untranslated regions of the cDNAs contain unusual poly(AT)n stretches that may play a role in the regulation of RNA stability. The protein encoded by agNt84 cDNA was expressed in Escherichia coli as a fusion with maltose-binding protein, and was shown to have the ability to bind to a nickel-chelating resin, indicating that it may function as a metal-binding protein.
从欧洲桤木根瘤的cDNA文库中分离出了代表富含甘氨酸和组氨酸蛋白的基因家族不同成员（agNt84和ag164）的两个cDNA。相应基因的表达仅在根瘤中检测到。通过原位杂交发现，根瘤中的表达发生在预固定区（2区）的年轻感染细胞中。编码的蛋白质含有用于靶向内膜系统的假定信号肽，与植物富含甘氨酸蛋白的信号肽具有序列相似性，其中包括大豆的一种根瘤特异性蛋白结节素24。这种相似性表明，与结节素-24类似，agNt84/ag164编码的蛋白质可能位于宿主植物膜与内共生体周围基质之间的界面处。cDNA的3'非翻译区含有不寻常的聚（AT）n序列，可能在RNA稳定性调节中起作用。agNt84 cDNA编码的蛋白质在大肠杆菌中作为与麦芽糖结合蛋白的融合蛋白表达，并显示出与镍螯合树脂结合的能力，表明它可能作为金属结合蛋白发挥作用。
