Kaien Li

Year of Award


Degree Type


Degree Name

Doctor of Philosophy (PhD)


Department of Biology.

Principal Supervisor

Xia, Yiji


Messenger RNA ; NAD (Coenzyme) ; Plants ; RNA-protein interactions ; Analysis




The DXO/RAI1 family proteins existed uniquely in eukaryotes are known to function in mRNA decapping and degradation. This protein family was initially identified as an exonuclease activator. However, further research found that it possesses canonical m7G-capped and noncanonical NAD-capped RNA decapping activities and exoribonuclease activity in yeast and mammals. In this study, it was found that Arabidopsis DXO1 possesses both NAD-RNA decapping and 5' to 3' exonuclease activities but lacks the m7G-capped RNA decapping activity. The loss of function of AtDXO1 enhances the stability of transfected NAD-RNA and slightly increases the amount of endogenous NAD-RNA in plants. However, the mutant's severe growth phenotype is independent on AtDXO1's NAD-RNA decapping activity. Yeast two hybrid screen identified multiple proteins that interact with AtDXO1. AtDXO1 interacts with an RNA cap methyl transferase (CMT) through its plant-specific N-terminus. Incompletely capped mRNA accumulated in the dxo1 mutant, indicating that AtDXO1 might bind to the 5' end of the mRNA facilitating the m7G cap processing. Structural analysis by cryo-EM showed that AtDXO1 can form a hexameric ring structure instead of previously reported monomeric form. This study provides important knowledge on the molecular functions of this important protein involved in RNA modification and degradation.


Principal supervisor: Professor Xia Yiji ; Thesis submitted to the Department of Biology ; Thesis (Ph.D.)--Hong Kong Baptist University, 2019.


Includes bibliographical references (pages 84-92)