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Restriction enzyme map of tobacco major rDNA units. Individual IGS subregions are termed as SR-II (containing C subrepeats), SR-VI (containing A1/A2 subrepeats), and SR-VII. Restriction enzymes delimiting the regions analyzed were as follows: B, BstNI; E, EcoRV; M, MboI; X, XbaI. Positions of target sites for methylation-sensitive enzymes are given in Table I. Distances are approximately to scale.
