Recent studies suggest that diverse types of intronic and small non-coding RNAs play pivotal regulatory roles, often as a part of ribonucleoprotein (RNP) complexes, in a variety of cellular proces-ses such as transcription and translation. Thus, isolation and char-acterization of novel RNP complexes, such as micro RNPs, small nuclear RNPs, small nucleolar RNPs, and heteronuclear RNPs, are crucial to understand the biological systems.