INTRON-LESS RNA INJECTED INTO THE NUCLEUS OF XENOPUS OOCYTES ACCESSESA REGULATED TRANSLATION CONTROL PATHWAY

The translation of a capped, polyadenylated RNA after injection into t he nucleus of Xenopus oocytes occurs only if the RNA contains an intro n. A single point mutation in the splice donor site prevents translati on. Intron-less RNA is exported efficiently to the cytoplasm and is he ld, undegraded, in a translationally inert state for several days. Tra nslation can be activated by treating the oocytes with progesterone or by injecting antibodies that bind the FRGY2 class of messenger RNA bi nding proteins, p56 and p60, but these antibodies are only effective i f delivered to the nucleus. Inhibitors of casein kinase II also activa te translation whereas phosphatase inhibitors block progesterone-media ted activation of translation. These data suggest the presence of an R NA handling pathway in the nucleus of Xenopus oocytes which is regulat ed by casein kinase type II phosphorylation and which directs transcri pts 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 re versed by progesterone treatment. These data may have implications for understanding translational control during early development.