An In Vitro Transcription System from BmN Cells of the Silkworm, Bombyx mori
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Eukaryotic RNA polymerase II requires a set of protein factors for the accurate initiation of gene transcription (1 ). Whole-cell and nuclear extracts containing these components have been prepared from cultured cells and used to execute faithful transcription initiation on the DNA templates (2 –7 ). Transcriptionally active extracts have also been obtained from embryos (5 , 8 ) and differentiated tissues (5 , 9 , 10 ). In order to facilitate studies of class II gene regulation in Lepidopteran insects, we developed a cell-free system from BmN cells, a cell line established from an ovarian tissue of the silkworm, Bombyx mori (7 , 11 ). The essential features of our in vitro transcription system may be summarized as follows:
