EN
The restriction enzyme analysis of III/2D and 6/42 strains and selected variants III/2D, III/2M, 6/42D and 6/42M selected at the presence of specific antibodies has been carried out. One additional fragment of 24 kbp was found after DNA digestion of the III/2D variant with Hind III enzyme. Electrophoretic patterns of DNA of the III/2D variant after digestion with Pst I and Eco RI enzymes revealed the lack of 6.2 kbp and 12.7 kbp fragments confirming the shifting of cleavage sites compared with parental DNA of the III/2 strain. No shifts in cleavage sites were observed in the case of Ш/2М, 6/42D and 6/42M DNAs. The data suggested that the increased resistance to nautralization with polyclonal antibody of the III/2D could result from genotype mutation.