FIG. 7.

Endogenous U18 snoRNA processing in the rat1-1 xrn1Δ mutant strain. Northern analysis of total RNA extracted from the untransformed rat1-1 xrn1Δ double mutant strain at different times after a shift to the nonpermissive temperature (hr-37°C) and hybridized with oligonucleotide I5′ (Fig. 1). The different products are indicated on the right, as in Fig. 2. Note that the migration of the I-3 molecule is faster than that of the debranched intron with respect to previous gels. This is due to the smaller size of the first exon of the endogenous EFB1 gene with respect to the ectopic constructs (101 and 201 nt, respectively). Lane M contained MspI-digested pBR322 plasmid DNA.