Rlp24蛋白質與60S核醣體出核因子的關連與影響

Study the Connection between Rlp24 and the Nuclear Export Factors of the 60S Ribosomal Subunits

李 寧(Ning Lee)

指導教授 ： 羅凱尹

國立臺灣大學/生物資源暨農學院/農業化學研究所/碩士(2014年)

https://doi.org/10.6342/NTU.2014.01448

摘要

真核生物的核醣體在核內進行預合成。其中pre-60S核醣體完成大部分結構蛋白的組合後，傳遞到細胞質中成熟 (maturation)，在此過程中釋放部分調控蛋白做最後修飾，形成具有完整轉譯功能的60S核醣體。而核醣體透過與核孔複合體(Nuclear pore complex)的相互作用運輸出核，其中pre-60S具有許多出核因子 (export factors)，如Mex67-Mtr2複合體透過與核孔蛋白 (nucleoporins) 的作用協助pre-60S出核；pre-60S也利用組成中的Nmd3作為受體與運輸蛋白Crm1結合，透過Ran-GTP梯度幫助pre-60S運輸出核；另一出核因子Arx1藉由結構上的非極性區域幫助pre-60S與NPC結合並通過；同時這些出核因子也提供生合成過程中的檢查與調控功能。
pre-60S上的其一調控蛋白Rlp24 (ribosomal-protein-like protein) 結構與組成蛋白L24類似，在pre-60S出核後會透過其延伸的C-terminus與ATPase Drg1反應並從pre-60S釋放，以利接下來的成熟步驟進行。本研究中發現，當Rlp24的C-terminus接上myc tag時，在nup120Δ或arx1Δ這類pre-60S出核缺失的突變株內，Rlp24-myc會造成細胞生長缺失與pre-60S的出核更加嚴重受阻。在進一步實驗結果中發現，NPC中的數個nucleoporins可能協助Drg1將Rlp24從pre-60S釋放的過程；另一方面，在NPC的nucleoporins產生缺失時，加入表現Mex67-Mtr2可能協助pre-60S的出核過程，進而幫助隨後發生的Rlp24的釋放過程。也因此當在nup120Δ或arx1Δ大量表現Rlp24-myc時，可能造成pre-60S成熟過程下游的調控蛋白無法正常在細胞質中被釋放，顯示pre-60S subunit正確的出核過程與下游的成熟過程是緊密連結的。

關鍵字

核醣體 ； 核醣體生合成 ； 核孔複合體 ； 出核途徑 ； Rlp24

並列摘要

Ribosomes biogenesis is a highly energy-consuming process in the cell. The synthesis starts from the nucleolus and matures in the cytoplasm, where ribosomes carry out protein translation. Ribosomes are very large complexes and cannot pass through the nuclear pore complex (NPC) on their own. In addition, the function of export receptors, including Mex67-Mtr2, Crm1and Arx1, is to help the ribosomal subunits out of the nucleus by assisting interaction between the ribosome and the NPC. Further, they also function as transacting factors and regulation points in ribosome biogenesis.
In this study, we found that C-terminal myc tag fusion Rlp24 (ribosomal-like protein 24) complemented the function of Rlp24 and did not show any negative effects in wild-type cells. However, it severely impaired the growth of the mutants with 60S export defects, including several nucleoporin mutants and other ribosome export mutants. In further examinations we found that none of these nucleoporins in NPC interact directly with Rlp24 yet show genetic interaction with RLP24. This suggests that these nucleoporins may participate in helping the release of Rlp24 by AAA-ATPase Drg1. On the other hand, if we overexpress Mex67 or Mtr2 in nup120Δ with Rlp24-myc, the dominant negative growth defects will be rescued. This result implicates possible interaction between Mex67-Mtr2 and Rlp24.
In addition, overexpression of Rlp24-myc caused other assembly factors such as Nog1, Mrt4 and Tif6 fail to be released from the pre-60S subunits and this defect was further enhanced when coupled with arx1Δ or nup120Δ, suggesting that the correct export process of pre-60S is important for the downstream maturation steps.

並列關鍵字

Ribosome ； ribosome biogenesis ； export ； Nuclear Pore Complex ； Rlp24

參考文獻

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