Functional of nucleolar AAA-ATPase NVL2 in ribosome biogenesis.

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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.