Kuchka M R, Goldschmidt-Clermont M, van Dillewijn J, Rochaix J D
Department of Plant, University of Geneva, Switzerland.
Cell. 1989 Sep 8;58(5):869-76. doi: 10.1016/0092-8674(89)90939-2.
The nuclear NAC2 locus of C. reinhardtii encodes a trans-acting factor that confers stability on the chloroplast message for the D2 protein of photosystem II (PS II). A mutant that carries a lesion in the NAC2 gene is unable to accumulate the psbD transcript encoding D2, but synthesizes all other PS II proteins normally. However, the PS II complex is completely unstable in the nac2-26 mutant, and all major PS II polypeptides, including the three oxygen-evolving enhancing proteins, are absent or greatly reduced in this strain because of posttranslational degradation. In C. reinhardtii the second exon of the trans-spliced psaA mRNA is cotranscribed with psbD (Choquet et al., 1988), but the nac2-26 mutation normally has no effect on psaA message maturation or stability. However, in double mutants carrying the nac2-26 mutation, as well as a mutation that prevents psaA splicing, splicing intermediates carrying psbD sequences are degraded. These results suggest that the NAC2 gene product acts in a very specific manner to control the half-life of psbD transcripts.
莱茵衣藻的核NAC2基因座编码一种反式作用因子，该因子赋予光系统II（PS II）D2蛋白的叶绿体信使稳定性。在NAC2基因中携带损伤的突变体无法积累编码D2的psbD转录本，但能正常合成所有其他PS II蛋白。然而，PS II复合物在nac2 - 26突变体中完全不稳定，并且由于翻译后降解，该菌株中所有主要的PS II多肽，包括三种放氧增强蛋白，都不存在或大量减少。在莱茵衣藻中，反式剪接的psaA mRNA的第二个外显子与psbD共转录（Choquet等人，1988），但nac2 - 26突变通常对psaA信使的成熟或稳定性没有影响。然而，在携带nac2 - 26突变以及阻止psaA剪接的突变的双突变体中，携带psbD序列的剪接中间体被降解。这些结果表明，NAC2基因产物以非常特定的方式控制psbD转录本的半衰期。
