Transcription of ribosomal RNA genes in mouse and frog

From information presented in this volume and elsewhere, it is now clear that major control of eukaryotic gene expression is exerted at the transcriptional level, apparently largely at the initiation step. Consequently, much interest is being devoted to analyzing the transcriptional process, both in vivo and in vitro. Studies in manipulable systems, especially those that utilize cloned DNA templates, are proving most fruitful. Systems in which RNA polymerase III mediates the accurate transcription of cloned 5 S RNA, VA RNA, and transfer RNA (tRNA) genes (Brown and Gurdon, 1977, 1978; Wu, 1978; Birkenmeier et al.,1978; Weil et al., 1979a) and systems in which RNA polymerase II accurately transcribes messenger RNA-coding genes (Weil et al., 1979b; Mulligan et al., 1979; Hamer and Leder, 1979; Grosschedl and Birnsteil, 1980a; Manley et al., 1980; McKnight and Gavis, 1980) have been developed in the last five years. From studies with these systems, many aspects of the nucleoprotein interactions that direct eukaryotic transcription—that is, the nucleotide sequences and the protein species that facilitate and regulate this process—are being elucidated (Sakonju et al.,1980; Bogenhagen et al.,1980; Grosschedl and Birnsteil, 1980b; Fowlkes and Shenk, 1980; Engelke et al., 1980; Honda and Roeder, 1980; McKnight et al.,1981; Hu and Manley, 1981; Wasylyk and Chambon, 1981; Hofstetter et al., 1981; Segall et al., 1981; Matsuei et al., 1981; McKnight and Kingsbury, 1982).