Figure 2.

Mapping of the 5′ and 3′ extremities of the pre-25S rRNAs. A, Structure of pre-25S intermediates identified by a set of primers (in shaded box). Forward and reverse PCR primers for cDNA amplification are marked in red and blue, respectively. Four pairs of primers were used for pre-25S rRNAs: 25P1 (25L/25R), 25P2 (p44/25R), 27P1 (58L/25R), and 27P2 (p4/25R). For each fragment, the number of clones obtained is indicated on the right. The number of clones containing additional sequences at the 3′ extremities is marked in parentheses. B, Pre-25S rRNA intermediates were determined in gel by cRT-PCR with primers 25P1, 25P2, 27P1, and 27P2. C to F, The DNA sequencing results for 25S (C) and its major precursors identified: 27SB (D), 27SA3 (E), and 27SA2 (F). The 25S rRNA identified by primers 25P1 were validated by sequencing of 20 independent clones (C). The 27SB intermediates identified by primers 25P2 and 27P1 were validated by sequencing of 51 independent clones (D). The 27SA3 intermediates identified by primers 27P1 and 27P2 were validated by sequencing of 22 independent clones (E). The 27SA2 intermediates identified by primers 27P2 were validated by sequencing of 21 independent clones (F). The ITS1 and ITS2 locus matched by the 5′ and 3′ ends of these DNA sequences, respectively, are indicated by black triangles as well as the number of clones. Additional sequences in the 3′ extremities of these clones are marked in red lowercase letters. The number of identical clones is indicated to the right of each fragment.