Regulator of pre-mRNA splicing (and, possibly, of other RNA processing events). Regulates its own expression at the level of RNA processing. Speckled subnuclear compartment. Three mRNAs are produced during development. The smallest of these (3.5 kb RNA) is the majority species during precellular blastoderm development after which its levels drop rapidly, but persists as a minority species throughout the rest of the life of the organism. The larger two transcripts (4.4 and 5.2 kb RNAs) first appear around cellular blastoderm and levels increase substantially during next few hours and are the preponderant RNA species throughout the remainder of the life of the organism. RS domain directs localization of proteins to the speckled subnuclear compartment and the purpose of this localization is to allow colocalization and co-concentration of components of the splicing and splicing regulatory machinery to permit relatively high rates and/or efficiencies of reaction and interaction.