Onouchi Hitoshi, Haraguchi Yuhi, Nakamoto Mari, Kawasaki Daisuke, Nagami-Yamashita Yoko, Murota Katsunori, Kezuka-Hosomi Azusa, Chiba Yukako, Naito Satoshi
Division of Applied Bioscience, Graduate School of Agriculture, Hokkaido University, Sapporo 060-8589, Japan.
Plant Cell Physiol. 2008 Apr;49(4):549-56. doi: 10.1093/pcp/pcn028. Epub 2008 Feb 19.
The Arabidopsis thaliana CGS1 gene encodes cystathionine gamma-synthase, the first committed enzyme of methionine biosynthesis in higher plants. Expression of CGS1 is feedback-regulated at the step of mRNA degradation in response to S-adenosyl-L-methionine (AdoMet). A short stretch of amino acid sequence, termed the MTO1 region, encoded within the first exon of CGS1 itself acts in cis in the regulation. In vitro analyses using wheat germ extract (WGE) revealed that AdoMet induces temporal translation arrest of CGS1 mRNA prior to mRNA degradation. This translational pausing occurs immediately downstream of the MTO1 region and is mediated by the nascent MTO1 peptide. In order to elucidate further the nature of this unique regulatory mechanism, we have examined whether a non-plant system also contains the post-transcriptional regulation activity. Despite the fact that mammals do not carry cystathionine gamma-synthase, AdoMet was able to induce the MTO1 sequence-dependent translation elongation arrest in rabbit reticulocyte lysate (RRL) in a similar manner to that observed in WGE. This result suggests that MTO1 peptide-mediated translation arrest does not require a plant-specific factor and rather most probably occurs via a direct interaction between the nascent MTO1 peptide and the ribosome that has translated it. In contrast, decay intermediates of CGS1 mRNA normally observed upon induction of CGS1 mRNA decay in plant systems were not detected in RRL, raising the possibility that CGS1 mRNA degradation involves a plant-specific mechanism.
拟南芥CGS1基因编码胱硫醚γ-合酶，这是高等植物中甲硫氨酸生物合成的首个关键酶。CGS1的表达在mRNA降解步骤受到S-腺苷-L-甲硫氨酸（AdoMet）的反馈调节。在CGS1自身第一个外显子内编码的一段短氨基酸序列，称为MTO1区域，在这种调节中起顺式作用。使用小麦胚芽提取物（WGE）进行的体外分析表明，AdoMet在mRNA降解之前诱导CGS1 mRNA发生暂时性翻译停滞。这种翻译暂停发生在MTO1区域的紧邻下游，并且由新生的MTO1肽介导。为了进一步阐明这种独特调节机制的本质，我们研究了非植物系统是否也具有转录后调节活性。尽管哺乳动物不携带胱硫醚γ-合酶，但AdoMet能够以与在WGE中观察到的类似方式在兔网织红细胞裂解物（RRL）中诱导MTO1序列依赖性的翻译延伸停滞。这一结果表明，MTO1肽介导的翻译停滞不需要植物特异性因子，很可能是通过新生的MTO1肽与翻译它的核糖体之间的直接相互作用发生的。相比之下，在植物系统中诱导CGS1 mRNA降解时通常观察到的CGS1 mRNA衰变中间体在RRL中未被检测到，这增加了CGS1 mRNA降解涉及植物特异性机制的可能性。
