The Epstein-Barr virus EBNA1 protein binds to G-quadruplexes in its own mRNA hence controlling its expression and immune evasion of the virus

The oncogenic Epstein-Barr virus (EBV) evades the immune system but has an Achilles heel: its genome maintenance protein (GMP) EBNA1, which is essential for viral genome replication, but also highly antigenic. Hence, the virus evolved a mechanism to limit the translation of EBNA1 mRNA to the minimum level which allows EBNA1 to fulfil its essential function while minimizing production of EBNA1-derived antigenic peptides. This mechanism involves the binding of the arginine-glycine-rich (RGG) motif of nucleolin (NCL), a host protein, to RNA G-quadruplexes (rG4) of the viral EBNA1 mRNA. This binding is dependent on arginine methylation of NCL RGG. EBNA1 contains two RGG motifs suggesting it could also be involved in this mechanism. Here we show that EBNA1 binds directly to rG4 of its own mRNA and limits its own expression, depending on its RGG motifs and their arginine methylation. Furthermore, EBNA1 and NCL cooperate to bind to rG4 of EBNA1 mRNA. As the GMP function of EBNA1 has been previously associated to its ability to bind RNA in an rG4-dependent manner, our results suggest the existence of a ternary EBNA1/NCL/EBNA1 mRNA protein/RNA complex that serves for both EBNA1 GMP function and capacity to auto-limit its expression to evade the immune system.