The Taka-amylase A gene (taaG2) of Aspergillus oryzae is inducibly expressed in A. nidulans upon exposure to inducing carbon sources, such as starch and maltose. In order to identify nuclear factor(s) possibly involved in the induction of the taaG2 gene, gel mobility shift assays and DNase I footprinting analyses were carried out, and revealed a novel nuclear factor in A. nidulans extracts, which specifically bound to two sites in the taaG2 promoter region, -204 to -189 and -182 to -168, which share the common sequence GGAAATT. The nuclear factor was detected in nuclei from both induced and uninduced mycelia. Mutational analysis within and around the binding sequences demonstrated that only the upstream binding sequence, designated SRE (starch responsive element), was required for the inducible expression of the taaG2 gene, and thus we designated the nuclear factor SREB (SRE binding factor). The downstream binding site contained an inverted SRE (ISRE) and played no role in the induction of taaG2 expression. SREB was shown by gel retardation assays to have higher affinity for SRE than for ISRE.

译文

米曲霉的Taka-淀粉酶A基因 (taaG2) 在暴露于诱导碳源 (如淀粉和麦芽糖) 后可在构巢曲霉中诱导表达。为了鉴定可能参与taaG2基因诱导的核因子,进行了凝胶迁移率位移测定和DNase I足迹分析,并在niddulans提取物中发现了一种新的核因子,该因子特异性结合到两个位点在taaG2启动子区域,-204至-189和-182至-168,它们共享公共序列ggaaaatt。在诱导和未诱导的菌丝体的细胞核中均检测到核因子。结合序列内和周围的突变分析表明,taaG2基因的诱导型表达只需要上游结合序列,称为SRE (淀粉反应元件),因此我们指定了核因子SREB (SRE结合因子)。下游结合位点包含反向SRE (ISRE),在诱导taaG2表达中不起作用。凝胶阻滞试验显示SREB对SRE的亲和力高于对ISRE的亲和力。

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