Nucleoli come undone

The nucleolus is essential for ribosome synthesis, cell cycle control, and telomerase sequestration. This complex of rDNA, RNA, and proteins disassembles around ovulation and later reassembles during early embryogenesis. Somatic nuclei transplanted into eggs during nuclear cloning also undergo nucleolar disassembly and reassembly—processes that may contribute to the low efficiency of nuclear transplantation cloning. Now, Koichi Gonda, Nobuaki Kikyo, and colleagues (University of Minnesota, Minneapolis, MN) find that, despite their complexity, nucleoli need only a small RNA-binding protein to make them fall apart.

Gonda et al. purified two proteins from frog egg cytoplasm, FRGY2a and FRGY2b, that have nucleolar disassembly activity. Recombinant versions of either protein dispersed nucleolar proteins and RNA, leaving only small nucleolar remnants. FRGY2a/b may release proteins bound to RNA within the nucleoli through nonspecific competition, as regions imparting nonselective charge...