Figure 3.

The ITS1 region is required for production of 25S RNA. (A) Structure of ITS1 deletion variants. The strategy used to construct these plasmids is described in Fig. 1A, along with details for construction of plasmids pWL180 and pWL184 (see Materials and Methods). Novel 3′-rDNA plasmids pWL208, -203, and -204 were prepared by subcloning appropriate PCR fragments into pWL155 after double digestion with XhoI and MluI. All rDNAs were expressed with GAL7 promoters and terminators. (B) Growth properties of cells containing the plasmid pairs shown in A. Phenotypes were analyzed on galactose medium, as described in Fig. 1B and are summarized in A. ± indicates extremely slow growth. (C) Northern hybridization analysis of rRNA expressed from the different split operons; details of the assay are provided in Fig. 1C. Levels of 18S and 25S RNA are tabulated in A.