Re‐evaluation of the site of transcription in Ehrlich tumour cell nucleoli

Abstract

Recent electron microscopic immunolocalization studies (Scheer and Rose, 1984) indicated that RNA polymerase I is located in, and probably confined to, the fibrillar centers of the nucleoli. This conclusion appears to be in contradiction to previous autoradiographic studies reporting that transcription of rRNA genes takes place in the dense fibrillar component. Despite the fact that rRNA transcription occurs in the dense fibrillar component of Ehrlich tumor cell nucleoli, we show in the present paper that dense fibrillar component containing rapidly labelled RNA can be visualized not only around but also inside the fibrillar centers.