College of Life Sciences, Northwest A&F University, Yangling 712100, Shaanxi, China.
J Plant Physiol. 2011 Oct 15;168(15):1780-3. doi: 10.1016/j.jplph.2011.04.001. Epub 2011 May 17.
The DnaJ proteins (also called as J proteins, J domain proteins or HSP40 proteins) function as molecular co-chaperones for the HSP70 proteins. We assessed the expression of the small chloroplast-targeted DnaJ protein, the AtJ8 protein, by subjecting the wild type Arabidopsis plants to different illumination conditions. It is shown that the expression of the transcripts and proteins of the ATJ8 gene is primarily regulated at the level of transcription. When plants were incubated under high light for 3h, both the transcripts and proteins were completely abolished. Upon transfer of plants to darkness, the transcripts started rapidly accumulating, and subsequently, the AtJ8 protein became visible after 2h in darkness. Conversely, incubation of plants in darkness or under low light intensities induced expression of the ATJ8 transcripts and proteins. Feeding plants with sugars clearly decreased the transcript and protein levels, and incubation with cycloheximide revealed a rapid turnover for AtJ8 in darkness. Moreover, the AtJ8 protein was found to be nearly missing from the var1 mutant, which lacks the FTSH5 protease. It is concluded that AtJ8 is expressed mainly in darkness, is prone to a rapid turnover but is partially stabilized by the FTSH proteases.
DnaJ 蛋白（也称为 J 蛋白、J 结构域蛋白或 HSP40 蛋白）作为 HSP70 蛋白的分子伴侣发挥作用。我们通过使野生型拟南芥植物处于不同的光照条件下，来评估小的质体靶向 DnaJ 蛋白 AtJ8 的表达情况。结果表明，ATJ8 基因的转录物和蛋白质的表达主要在转录水平上受到调控。当植物在强光下孵育 3 小时时，转录物和蛋白质完全被消除。当植物转移到黑暗中时，转录物迅速开始积累，随后在黑暗中 2 小时后可见到 AtJ8 蛋白。相反，在黑暗或低光照强度下孵育植物会诱导 ATJ8 转录物和蛋白质的表达。用糖喂养植物明显降低了转录物和蛋白质的水平，用环己酰亚胺孵育表明 AtJ8 在黑暗中快速周转。此外，在缺乏 FTSH5 蛋白酶的 var1 突变体中几乎检测不到 AtJ8 蛋白。结论是，AtJ8 主要在黑暗中表达，容易快速周转，但部分被 FTSH 蛋白酶稳定。
