Functional of nucleolar AAA-ATPase NVL2 in ribosome biogenesis.

NVL 2是AAA-ATP酶家族的成员，其调节蛋白质复合物的功能。NVL 2与核糖体蛋白L5和RNA解旋酶DOB 1相互作用，参与60 S核糖体的生物合成。为了研究NVL 2在核糖体生物发生中的作用，已经进行了以下研究。1.已经证明，通过表达NVL 2的显性负突变体，60 S核糖体的生物合成受损。为了研究这些细胞中rRNA前体的加工是否受损，进行了北方印迹和脉冲追踪分析。这些实验对rRNA前体的加工没有明显的影响。这些结果表明，NVL 2参与了核糖体生物合成的后期步骤完成后的rRNA前体的加工。2.利用蔗糖梯度分离培养细胞核提取物，分析NVL 2和DOB 1与前核糖体之间的相互作用。结果表明，NVL 2与核内的前核糖体相互作用。相反，在与前核糖体相同的组分中没有观察到DOB，而在低分子量组分中存在DOB。然而，在显性负性NVL 2表达的细胞中，DOB 1的一部分出现在前60 S核糖体的组分中。这些结果表明NVL 2可能作为分子伴侣，调节DOB 1和前核糖体之间的相互作用。

NVL2 is a member of the AAA-ATPase family, which regulates functions of protein complexes. It has been shown that NVL2 interacts with ribosomal protein L5 and RNA helicase DOB1 and is involved in the biogenesis of 60S ribosome. To investigate the role of NVL2 in ribosome biogenesis, following studies have been done. 1. It has been demonstrated that biogenesis of 60S ribosome is impaired by expressing a dominant negative mutant of NVL2. To investigate whether processing of rRNA precursor is impaired in these cells, Northern blotting and pulse-chase analysis were performed. These experiments did not show distinct effect on the processing of rRNA precursor. These results suggest that NVL2 is involved in a late step of ribosome biogenesis after the completion of the processing of rRNA precursors. 2. Interactions between preribosome and NVL2 or DOB1 were analyzed by using sucrose gradient fractionation of nuclear extracts from cultured cells. The results demonstrated that NVL2 interacts with preribosome in the nucleus. On the contrary, DOB was not observed in the same fractions with preribosome and existed in the low molecular weight fractions. However, in cells in which the dominant negative NVL2 is expressed, a part of DOB1 was appeared in the fractions of pre-60S ribosomes. These results suggest that NVL2 might act as a molecular chaperone, which regulates interaction between DOB1 and preribosome.