Figure 4. The EJC enhances p53 protein expression.

(A) HeLa cells were transfected with the empty or FLAG-Y14 or eIF4A3 expression vector. Immunoblotting of p53, FLAG-tagged proteins, and α-tubulin, and RT-PCR of p53 and GAPDH are shown. Asterisk indicates p53β. (B) Immunoprecipitation was performed using anti-FLAG in HeLa cells transfected as in panel A. Co-precipitated RNA was analyzed by RT-PCR for p53 and small nuclear RNA U6 (control). The asterisk indicates a non-specific co-precipitate. (C) Model shows cis- and trans-regulation of p53 splicing. Exon i9 inclusion is in part determined by 5′ splice site strengths (see Discussion). Moreover, Y14 prevents exon i9 inclusion via association of the EJC with a downstream spliced exon or when it is tethered downstream. After splicing, the EJC may subsequently participate in the translation of p53 mRNA to ensure efficient p53 protein production.