Bcp1和甲基轉移酶Rkm1協同調控核醣體蛋白Rpl23的穩定性

Bcp1 and methyltransferase Rkm1 regulate the stability of ribosomal protein Rpl23 coordinately

謝境梃(Jing-Ting Shie)

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(2017年)

https://doi.org/10.6342/NTU201703627

摘要

核醣體生合成的過程中，會有約略200個合成因子參與其中，這些因子主要的功用在幫助核醣體生成、修飾、組裝、以及品質的調控，讓核醣體能夠正確生成。我們實驗室之前發現Bcp1是核醣體蛋白Rpl23的伴護蛋白，具有保護Rpl23結構穩定的功能。我進一步研究發現Bcp1會將剛入核的Rpl23從運輸蛋白(Karyopherins) 上釋放，並和其結合，來確保Rpl23以正確構型結合到核醣體大單元60S上。從前人研究中知道Rkm1是甲基轉移酶，具有將Rpl23上的106與110的離胺酸雙甲基化(dimethylation)的功能，但其甲基化所造成的生理意義尚未被解開。本研究結果發現Rkm1需要Rpl23才會與運輸蛋白結合，一同運輸入核，之後和Bcp1形成三聚體，而Bcp1會活化Rkm1對Rpl23 lysine110的甲基化，在Rpl23甲基化順利完成後，會與Bcp1一同從Rkm1上釋放，接著組裝到60S上。Rkm1缺失時對細胞的生長速度並無明顯影響，但在bcp1突變株中去除Rkm1時，會產生更嚴重的生長缺失，實驗結果發現，Rpl23蛋白質的量於雙突變株中的減少比bcp1突變株更加明顯，證明兩者間有功能上的關聯性，推測為協同保護Rpl23的穩定性。

關鍵字

核醣體 ； Bcp1 ； Rkm1 ； Rpl23 ； 核醣體蛋白 ； 甲基化 ； 伴護子

並列摘要

There are about 200 biogenesis factors participate in the ribosome biosynthesis.These biogenesis factors possess multiple functions such as facilitating the synthesis of ribosome, modifications of rRNAs or ribosomal proteins, assembly of the complex, and quality control of the ribosome. In our previous study, we find that Bcp1 is a chaperone of Rpl23, which can protect and stabilize the structure of Rpl23. In my study, I discover that Bcp1 can release Rpl23 from Karyopherins just after they were imported to nucleus and bind Rpl23 subsequently to ensure incorperation of Rpl23. Rkm1 has been shown as a methyltransferase of Rpl23, adding dimethylation to lysine106 and lysine110. But the physiological significance of lysine methylation stays unclear. Here, I found that Rkm1 co-transport with Rpl23 to nucleus and released by Bcp1. Bcp1, Rkm1 and Rpl23 form hetero-trimer, meanwhile Bcp1 triggers dimethylations on Rpl23 via Rkm1. After accomplishment of dimethylations, Rpl23/Bcp1 complex leaves Rkm1 and delivers Rpl23 to pre-60S. Deletion of RKM1 did not show growth defect, but synthetic growth deficiency was observed in bcp1ts and rkm1Δ double mutant. Moreover, the level of Rpl23 decreased even lower in double mutant. This suggests that both Bcp1 and Rkm1 have functions in protecting the stability of Rpl23.

並列關鍵字

Ribsome ； Bcp1 ； Rpl23 ； Rkm1 ； ribosomal protein ； methylation ； chaperone

參考文獻

陳柏儒. 2012. Bcp1蛋白在出芽酵母中核醣體生合成途徑之研究 Bcp1 is a protein involved in ribosome biogenesis in Saccharomyces cerevisiae. 農業化學系. Vol. 碩士論文. 國立臺灣大學, 台北.

丁亞涵. 2014. Bcp1、Rpl23及Sqt1形成的小複合體於核醣體生合成的功能研究。蛋白在出芽酵母中核醣體生合成途徑之研究 Functional characterization of the small complex containing Bcp1, Rpl23 and Sqt1 in ribosome biogenesis. 農業化學系. Vol. 碩士論文. 國立臺灣大學, 台北.

呂庭郡. 2015. Bcp1與Rpl23間交互作用之探討 Functional characterization of the interaction between Bcp1 and Rpl23. 農業化學系. Vol. 碩士論文. 國立臺灣大學, 台北.

Allmang, C., P. Mitchell, E. Petfalski, and D. Tollervey. 2000. Degradation of ribosomal RNA precursors by the exosome. Nucleic acids research. 28:1684-1691.

Audhya, A., and S.D. Emr. 2002. Stt4 PI 4-kinase localizes to the plasma membrane and functions in the Pkc1-mediated MAP kinase cascade. Dev Cell. 2:593-605.