R. Gururajan et al., AN3 MESSENGER-RNA ENCODES AN RNA HELICASE THAT COLOCALIZES WITH NUCLEOLI IN XENOPUS-OOCYTES IN A STAGE-SPECIFIC MANNER, Proceedings of the National Academy of Sciences of the United Statesof America, 91(6), 1994, pp. 2056-2060
An3 is a maternal mRNA localized to the animal hemisphere of oocytes a
nd early embryos. We have analyzed the enzymatic activity and the subc
ellular localization of the protein encoded by An3 mRNA during Xenopus
oogenesis. Antibodies raised using recombinant full-length and trunca
ted An3 protein recognized a single protein in Xenopus and single prot
eins from HeLa cells, Drosophila, mouse testes, and Saccharomyces cere
visiae. An3 protein immunoprecipitated from stage IV and stage VI oocy
tes had ATP-dependent RNA helicase activity. The subcellular location
of An3 protein changed during oocyte development. In previtellogenic o
ocytes, An3 was present throughout the nucleus; cytoplasmic localizati
on was relatively sparse. Nuclear localization in mid-vitellogenic ooc
ytes was primarily nucleolar; cytoplasmic staining increased relative
to earlier stages. In stage VI oocytes, An3 protein was detected only
in the cytoplasm. The temporal change in An3 protein localization is c
onsistent with a role in the production of large maternal pools of rRN
A during oogenesis.