Fig. 3. Northern blot analysis of extracts from ASBVd-infected UV-irradiated avocado leaves. Extracts were fractionated by denaturing PAGE and hybridized with a probe for detecting (+) viroid strands. (A) Partition after treatment with phenol/chloroform. Lane 1, crude extract; lanes 2, 3 and 4, fractions corresponding to the aqueous phase, interphase and organic phase, respectively. The interphase and organic phase fractions were concentrated 20-fold by alcohol precipitation with respect to the crude extract and the aqueous phase fraction. (B) Proteinase K digestion of a preparation enriched in adducts 3 and 4 derived from the concentrated interphase fraction. Lane 1, control of crude extract; lanes 2, 3 and 4, preparation untreated, incubated in buffer without proteinase K, and digested with proteinase K, respectively. The preparation enriched in adducts 3 and 4 was obtained by cutting a segment of a non-denaturing polyacrylamide gel and eluting its contents. The positions of the different ASBVd (+) RNAs and of the four ASBVd–protein cross-linked adducts are indicated on the left and right sides of both panels. Other details as in the legend to Figure 1.