RNA Pol I and RNA pol III produce the ribosomal RNAs that are assembled with proteins into ribosomes. Ribosomal transcription is important for cell growth and is, therefore, regulated during the cell cycle, during differentiation, and in different cell states. We have isolated a chromatin remodelling complex, B-WICH, that is involved in pol I and pol III transcription. The complex consists of the ATPase ISWI, the WSTF protein, nuclear myosin I and several ribosomal RNA processing proteins. It also contains RNA. We are now interested in studying which steps in rRNA synthesis require B-WICH, and whether the B-WICH is involved in the regulation of ribosomal transcription.