ORGANIZATION AND STRUCTURE OF NADH-DEPENDENT GLUTAMATE SYNTHASE GENE FROM RICE PLANTS

Genomic clones for NADH-dependent glutamate synthase (NADH-GOGAT; EC 1 .4.1.14) were obtained from a genomic library of rice (Oryza sativa L. cv. Sasanishki). A genomic clone (lambda OS42, 14 kb) covered an enti re structural gene and a 3.7 kb 5'-upstream region from the first meth ionine. Another clone (lambda OS23, 14 kb) contained a 2.8 kb 3'-downs tream region from the stop codon. A 7047 bp long clone (lambda OSR51) consisting of full length cDNA for NADH-GOGAT was isolated from a cDNA library prepared using mRNA from roots of rice seedlings treated with 1 mM NH4Cl for 12 h. The presumed transcribed region (11.7 kb) consis ted of 23 exons separated by 22 introns. Rice NADH-GOGAT is synthesize d as a 2166 amino acid protein with a molecular mass of 236.7 kDa that includes a 99 amino acid presequence. DNA gel blot analysis suggested that NADH-GOGAT occurred as a single gene in rice. Primer extension e xperiments map the transcription start of NADH-GOGAT to identical posi tions. The 3.7 kb 5'-upstream region was able to transiently express a reporter gene in cultured rice cells. Putative motifs related to the regulation of NADH-GOGAT gene expression were looked for within the 5' -upstream region by database. (C) 1998 Elsevier Science B.V. All right s reserved.