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

利用10日龄水稻幼苗制备的poly(A)^+RNA构建cDNA文库。我分离了三个核基因，rpl9、rpl12-1、rpl12-2、rpl13、rpl15、rp121、rpl24、rpl28、rps1和rps9，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，在水稻分子连锁图谱上定位了这些核编码基因。7个基因座分别位于水稻的5条染色体上。它们不是聚集在一起的，而是分散在水稻基因组中。通过Northern blotting对rpl12-1、rpl12-2、rpl13、rpl24的表达分析发现，这些基因在光照条件下均在10 d龄水稻幼苗叶片中表达，而在根系中不表达。这些数据表明核编码的核糖体蛋白基因以器官特异性的方式表达。分离rpl13和rpl24的基因组克隆，通过S1-nulcease定位和引物延伸确定转录起始位点。这表明这两个基因都有多个转录起始位点，并且每个位点在特定器官中用于转录起始的位点不同。

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.