Fine mapping of preS deletions. A. Alignment of detected preS deletions in HBV spreading in northern China (upper panel) with the mutations in the same region from 6 immune-suppressed kidney-transplant patients from a previous study (middle panel) . Known B- and T-cell epitopes in the preS region  are numbered from N- to C-terminus. Note the dramatic difference in deletion break points of preS2 and the higher deletion frequency at the 5′ terminus of preS1 between the two sample groups. The T- and B-cell epitopes of surface proteins are indicated in the bottom panel. B. PreS deletion patterns and their frequencies (right bars in black) in HBV prevailing in northern China. Sorting of 70 mutant clones resulted in four single patterns (I-IV) and four complex patterns as type I, start codon defect of L protein; type II, internal deletion of preS1; type III, start codon defect of M protein; and type IV, internal deletion of preS2. Gray bars indicate deletion positions. Blunt terminuses illustrate consistent break points and dotted edges display variable ends of deletions. Dashed lines show start codons in preS1 and preS2. Bars in black, right panel: The counts of different deletion patterns.