Lee W C, Zabetakis D, Mélèse T
Department of Biological Sciences, Columbia University, New York, New York 10027.
Mol Cell Biol. 1992 Sep;12(9):3865-71. doi: 10.1128/mcb.12.9.3865-3871.1992.
NSR1 is a yeast nuclear localization sequence-binding protein showing striking similarity in its domain structure to nucleolin. Cells lacking NSR1 are viable but have a severe growth defect. We show here that NSR1, like nucleolin, is involved in ribosome biogenesis. The nsr1 mutant is deficient in pre-rRNA processing such that the initial 35S pre-rRNA processing is blocked and 20S pre-rRNA is nearly absent. The reduced amount of 20S pre-rRNA leads to a shortage of 18S rRNA and is reflected in a change in the distribution of 60S and 40S ribosomal subunits; there is no free pool of 40S subunits, and the free pool of 60S subunits is greatly increased in size. The lack of free 40S subunits or the improper assembly of these subunits causes the nsr1 mutant to show sensitivity to the antibiotic paromomycin, which affects protein translation, at concentrations that do not affect the growth of the wild-type strain. Our data support the idea that NSR1 is involved in the proper assembly of pre-rRNA particles, possibly by bringing rRNA and ribosomal proteins together by virtue of its nuclear localization sequence-binding domain and multiple RNA recognition motifs. Alternatively, NSR1 may also act to regulate the nuclear entry of ribosomal proteins required for proper assembly of pre-rRNA particles.
NSR1是一种酵母核定位序列结合蛋白，其结构域结构与核仁素具有显著相似性。缺乏NSR1的细胞是有活力的，但存在严重的生长缺陷。我们在此表明，NSR1与核仁素一样，参与核糖体生物合成。nsr1突变体在rRNA前体加工方面存在缺陷，导致最初的35S rRNA前体加工受阻，且几乎不存在20S rRNA前体。20S rRNA前体数量的减少导致18S rRNA短缺，并反映在60S和40S核糖体亚基分布的变化上；不存在游离的40S亚基池，且60S亚基的游离池大小大幅增加。缺乏游离的40S亚基或这些亚基的组装不当导致nsr1突变体在不影响野生型菌株生长的浓度下，对抗生素巴龙霉素表现出敏感性，巴龙霉素会影响蛋白质翻译。我们的数据支持这样一种观点，即NSR1参与前体rRNA颗粒的正确组装，可能是通过其核定位序列结合结构域和多个RNA识别基序将rRNA和核糖体蛋白聚集在一起。或者，NSR1也可能起到调节前体rRNA颗粒正确组装所需核糖体蛋白进入细胞核的作用。
