Intron-less RNA injected into the nucleus of Xenopus oocytes accesses a regulated translation control pathway

The translation of a capped, polyadenylated RNA after injection into the nucleus of Xenopus oocytes occurs only if the RNA contains an intron. A single point mutation in the splice donor site prevents translation. Intron-less RNA is exported efficiently to the cytoplasm and is held, undegraded, in a translationally inert state for several days. Translation can be activated by treating the oocytes with progesterone or by injecting antibodies that bind the FRGY2 class of messenger RNA binding proteins, p56 and p60, but these antibodies are only effective if delivered to the nucleus. Inhibitors of casein kinase II also activate translation whereas phosphatase inhibitors block progesterone-mediated activation of translation. These data suggest the presence of an RNA handling pathway in the nucleus of Xenopus oocytes which is regulated by casein kinase type II phosphorylation and which directs transcripts to be sequestered by p56/p60 or by closely related proteins. This pathway can be bypassed if the RNA contains an intron and it can be reversed by progesterone treatment. These data may have implications for understanding translational control during early development.