Baima S, Haegi A, Strøman P, Casadoro G
Dipartimento di Biologia, II Università di Roma, Italy.
Carlsberg Res Commun. 1989;54(1):1-9. doi: 10.1007/BF02910467.
A barley cDNA clone (1182 bp) encoding chloroplastic glutamine synthetase was isolated with a heterologous cDNA probe of the gene specifying the enzyme from alfalfa. The clone, named pGS8, was found in a lambda gtII cDNA library prepared from dark grown barley leaves even though the chloroplastic glutamine synthetase is absent from such leaves. In agreement therewith the clone hybridized in Northern blot analyses with a 1.7 kb mRNA species present the in poly A+ mRNA fraction of both dark grown and greened primary leaves of barley. The nucleotide sequence of the barley clone reveals 75% identity to the Phaseolus vulgaris and Pisum sativum clones encoding chloroplastic glutamine synthetase, while only 69% identity is observed in comparisons with the clones specifying the cytosolic isozymes. At the amino acid level 85% identity is found between the deduced barley glutamine synthetase sequence and that of the corresponding chloroplastic isoenzymes from bean and pea. The chloroplastic glutamine synthetases contain cysteins in the putative ATP and and substrate binding sites. In the cytosolic forms these positions are occupied by alanine residues.
用来自苜蓿的编码该酶的基因的异源cDNA探针，分离出了一个编码叶绿体谷氨酰胺合成酶的大麦cDNA克隆（1182 bp）。该克隆名为pGS8，是在从黑暗生长的大麦叶片制备的λgtII cDNA文库中发现的，尽管此类叶片中不存在叶绿体谷氨酰胺合成酶。与此一致的是，在Northern印迹分析中，该克隆与大麦黑暗生长和绿化后的初生叶片的多聚A + mRNA组分中存在的1.7 kb mRNA物种杂交。大麦克隆的核苷酸序列与编码叶绿体谷氨酰胺合成酶的菜豆和豌豆克隆显示出75%的同一性，而与编码胞质同工酶的克隆相比，同一性仅为69%。在氨基酸水平上，推导的大麦谷氨酰胺合成酶序列与来自豆类和豌豆的相应叶绿体同工酶的序列有85%的同一性。叶绿体谷氨酰胺合成酶在假定的ATP和底物结合位点含有半胱氨酸。在胞质形式中，这些位置被丙氨酸残基占据。
