7SL RNA POLYMORPHISM IN HOP (HUMULUS-LUPULUS L)

Signal recognition particle (7SL RNA)- specific DNA sequences were amp lified by PCR from genomic DNA of hop, using 17-base primers derived f rom two conservative elements close to 5' (overlapping promoter box A) and 3' ends of the 7SL RNAs. When analysed on a 2.5% agarose gel the PCR products showed an apparently homogeneous band of 230 bp. These 23 0 bp products were cloned and sequenced. A 7SL RNA-specific riboprobe (designated 7SR) was prepared for further analysis of 7S RNA by molecu lar hybridization. This riboprobe sequence was fully complementary to positions 20-250 of 7SL RNA from the hop cv. Spalter described earlier in the GenBank (AC X65985) as sequence S10o. Using Northern blot anal ysis, we found that sequences complementary to the 7S riboprobe are hi ghly expressed in all hop cultivars examined, including Bohemian Osval d's clones 72 and 31, cultivars Wye Challenger, Yeoman, and samples No nsuch OM26 and Nonsuch OB53. For N. tabacum cv. White Burley we found about 25 times weaker signal suggesting low homology between 7SL RNA f rom hop and tobacco. For Further analyses LiCl-soluble RNA was extract ed from viroid-free clone Osvald 72 and cv. Yeoman and additionally fr actionated by precipitation in 20% of PEG 6000 in order to enrich low molecular weight RNAs. Using these extracts, we examined 7SR hybridizi ng sequences by temperature gradient gel electrophoresis (TGGE). This analysis revealed many individual melting points and transition curves , indicating a high variability of 7S RNA and suggesting presence of d ifferent closely related 7S RNA variants. Moreover, the hop cultivars examined clearly differed in TGGE patterns of 7SL RNA, suggesting appa rent polymorphism of these RNAs in hop.