Nuclear speckles (speckles) represent a distinct nuclear compartment within the 
interchromatin space and are enriched in splicing factors. In a previous study 
(Melcák et al., 2001), it has been shown that the pre-spliceosomal assembly on 
microinjected splicing-competent precursor mRNA takes place in the speckles, and 
it has been suggested that the targeting of RNA into speckes 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.