Nuclear encoded chloroplast ribosomal protein genes ; genomic structure and organ-specific gene expression.

以10天龄水稻幼苗为材料，用Poly(A)^+RNA构建了一个cDNA文库。我已分离到三个核基因rpl9、rpl12-1、rpl12-2、rpl13、rpl15、rp121、rpl24、rpl28、rps 1和rps 9，它们分别编码叶绿体核糖体蛋白L9、L12、L13、L15、L21、L24、L28、S1和S9。以这些克隆为探针，将这些核编码基因定位在水稻分子连锁图谱上。7个基因座位于水稻的5条不同染色体上。通过Northern blotting对rpl12-1、rpl12-2、rpl13、rpl24基因的表达分析表明，这些基因在10日龄水稻幼苗叶片中表达，而在根中不表达。这些数据表明，核糖体蛋白基因以器官特异的方式表达。分离了RPL13和RPL24的基因组克隆，并通过S1-nulce定位和引物延伸确定了转录起始点。推测这两个基因都有多个转录起始点，而且在特定器官中每个起始点的转录起始点是不同的。

A cDNA library was constructed with poly(A)^+RNA prepared from 10-day-old rice seedlings. I have isolated three nuclear genes, rpl9, rpl12-1, rpl12-2, rpl13, rpl15, rp121, rpl24, rpl28, rps1 and rps9, that encode chloroplast ribosomal proteins L9, L12, L13, L15, L21, L24, L28, S1 and S9 respectively. Using these clones as probes, these nuclear encoded genes were located on molecular linkage map of rice. Seven loci were located on 5 differnt chromosomes of rice. They were not clustered but dispersed throughout the rice genome.Expression analysis of rpl12-1, rpl12-2, rpl13, rpl24 by Northern blotting reveals that these genes were expessed in leaves of 10-day-old rice seedlings regardless of the presence of light, but not in roots. These data suggest that nuclear encoded ribosomal protein genes were expressed in an organ specific manner.The genomic clones of rpl13 and rpl24 were isolated, and transcription start sites were determined by S1-nulcease mapping and primer extension. It is suggested that both genes have multiple sites of transcription initiation, and that each site was employed for transcription initiation differently in specific organ.