Bouche G, Caizergues-Ferrer M, Bugler B, Amalric F
Nucleic Acids Res. 1984 Apr 11;12(7):3025-35. doi: 10.1093/nar/12.7.3025.
The synthesis of preribosomal RNA is inhibited "in vivo" and "in vitro" by the protease inhibitor leupeptin. "In vivo" leupeptin decreases by 74% the incorporation of labeled uridine into 45S pre rRNA while the synthesis of other RNA species is only slightly decreased. "In vitro", the elongation of already initiated pre rRNA chains that is achieved by incubation of isolated nucleoli is blocked by leupeptin. On the other hand, "in vitro" leupeptin has no direct effect on RNA polymerase I, tested in a nonspecific transcriptional system with Calf thymus DNA as template and in run off experiments with a cloned DNA containing the initiation site of the rDNA gene. A 100 kDa nucleolar protein which has been shown to be endoproteolytic cleaved "in vivo" (1) acts as an inhibitor of rDNA transcription in presence of leupeptin but produces little effect on the nonspecific transcription. In absence of the drug, the 100 kDa protein is processed in specific peptides which appeared to be similar to the "in vivo" maturation products. The possible role of the 100 kDa maturation process in the regulation of rDNA transcription is discussed.
蛋白酶抑制剂亮肽素在“体内”和“体外”均能抑制前核糖体RNA的合成。在“体内”，亮肽素可使标记尿苷掺入45S前体rRNA的量减少74%，而其他RNA种类的合成仅略有减少。在“体外”，通过分离核仁孵育实现的已起始前体rRNA链的延伸被亮肽素阻断。另一方面，在以小牛胸腺DNA为模板的非特异性转录系统以及使用含有rDNA基因起始位点的克隆DNA进行的径流实验中测试发现，亮肽素在“体外”对RNA聚合酶I没有直接影响。一种已被证明在“体内”会发生内切蛋白水解切割的100 kDa核仁蛋白，在亮肽素存在的情况下作为rDNA转录的抑制剂，但对非特异性转录影响很小。在没有该药物的情况下，100 kDa蛋白会被加工成特定的肽段，这些肽段似乎与“体内”成熟产物相似。本文讨论了100 kDa成熟过程在rDNA转录调控中的可能作用。
