Figure 10.

Proposed Roles for RRP7 in 45S pre-rRNA Processing Based on the Molecular Phenotype of the rrp7 Mutants.

Red arrows indicate over-accumulated (↑↑↑) or depleted (↓) pre-rRNAs, as detected by RNA gel blots and circular RT-PCR assays using the rrp7 mutants. In our model, Arabidopsis RRP7 is assumed to participate in the steps of 45S pre-rRNA processing in which the substrate is overaccumulated in the rrp7 mutants (P′, P₁ and C₂ cleavages; orange ovals). The question mark in C₂ cleavage (bottom middle) indicates that overaccumulation of 27SB pre-rRNA can alternatively be explained as an indirect effect of impaired 18S rRNA production. RRP7 might also participate in the steps in which the product is depleted in the rrp7 mutants (P₂ cleavages; gray ovals). Because RRP7 participates in the P′ cleavage at the 5′-ETS-first pathway, it might also cleave the same site at the ITS1-first pathway (yellow oval). Short-lived pre-rRNAs are shown in faint colors. Other details are as shown in Supplemental Figure 2.