An ATP-dependent step is required for the translocation of microinjected precursor mRNA into nuclear speckles

Nuclear speckles (speckles) represent a distinct nuclear compartment within the interchromatin space and are enriched in splicing factors. In a previous study (Melčák et al., 2001), it has been shown that the prespliceosomal assembly on microinjected splicing-competent precursor mRNA takes place in the speckles, and it has been suggested that the targeting of RNA into speckles consists of two interdependent steps, namely the diffusion process, followed by the energy-dependent translocation of RNA into the speckles. In the present study, we confirm the existence of these two steps and show that this latter translocation is ATP dependent.