merase (EC 2.7.7.6) have been demonstrated in eukaryotic cells (Roeder & Rutter, 1969; Jacob et al., 1970a; Kedinger et al., 1970; Mondal et al., 1970; Horgen & Griffin, 1971; Strain et al., 1971). RNA polymerase I (or A), which is associated with the nucleolus (Roeder & Rutter, 1970), is probably engaged in the transcription of nucleolar genes to form rRNA (Blatti et al., 1970; Tocchini-Valent...