Figure 1.

Ribosomal RNA processing in Saccharomyces cerevisiae. The 35S rRNA primary transcript undergoes several internal cleavages to produce the processing intermediates shown. Additional cleavages produce the mature 18S and 25S rRNAs and 5′- and 3′-end trimming reactions participate in the formation of 5.8S rRNA. 5S rRNA is produced from an independent transcription unit and is not shown. Numbered bars above the 35S pre-rRNA indicate the approximate positions of oligonucleotide probes used in the experiments described.