Kropat J, von Gromoff E D, Müller F W, Beck C F
Institut für Biologie III, Albert-Ludwigs-Universität, Freiburg, Germany.
Mol Gen Genet. 1995 Oct 25;248(6):727-34. doi: 10.1007/BF02191713.
Induction of HSP70 heat shock genes by light has been demonstrated in Chlamydomonas. Our aim was to establish whether this induction by light is mediated by the heat stress sensing pathway or by an independent signal chain. Inhibitors of cytoplasmic protein synthesis revealed an initial difference. Cycloheximide and other inhibitors of protein synthesis prevented HSP70A induction upon illumination but not during heat stress. Analysis of HSP70A induction in cells that had differentiated into gametes revealed a second difference. While heat shock resulted in elevated HSP70A mRNA levels, light was no longer able to serve as an inducer in gametes. To identify the regulatory sequences that mediate the response of the HSP70A gene to either heat stress or light we introduced a series of progressive 5' truncations into its promoter sequence. Analyses of the levels of mRNA transcribed from these deletion constructs showed that in most of them the responses to heat shock and light were similar, suggesting that light induction is mediated by a light-activated heat shock factor. However, we show that the HSP70A promoter also contains cis-acting sequences involved in light induction that do not participate in induction by heat stress. Together, these results provide evidence for a regulation of HSP70A gene expression by light through a heat shock-independent signal pathway.
衣藻中已证实光可诱导HSP70热休克基因。我们的目的是确定这种光诱导是由热应激传感途径介导还是由独立的信号链介导。细胞质蛋白质合成抑制剂显示出一个初始差异。环己酰亚胺和其他蛋白质合成抑制剂可阻止光照时HSP70A的诱导，但在热应激期间则不会。对已分化为配子的细胞中HSP70A诱导的分析揭示了第二个差异。虽然热休克导致HSP70A mRNA水平升高，但光在配子中不再能够作为诱导剂。为了鉴定介导HSP70A基因对热应激或光反应的调控序列，我们在其启动子序列中引入了一系列渐进的5'端截短。对这些缺失构建体转录的mRNA水平的分析表明，在大多数构建体中，对热休克和光的反应相似，这表明光诱导是由光激活的热休克因子介导的。然而，我们表明HSP70A启动子还包含参与光诱导的顺式作用序列，这些序列不参与热应激诱导。总之，这些结果为光通过热休克非依赖信号途径调控HSP70A基因表达提供了证据。
