The effect of the gene encoding EcoRII DNA methyltransferase on the phenotype of transgenic tumor cell lines of Nicotiana tabacum and the methylationlevel of CpNpG sequences in their genome

Several tumor cell lines were obtained by transforming Nicotiana tabacum pl ants with the recombinant Ti plasmid comprising the gene encoding EcoRII DN A methyltransferase (M.EcoRII) and subjected to analysis. The transformed l ines differed in their morphology, growth dependence on hormones, and nopal ine-synthesizing capacity. Southern blot-hybridization showed that the M.Ec oRII gene was present in the cells of all transformed lines. However, genom e analysis using polymerase chain reaction with the oligonucleotide primers recognizing 5'-ends of the M.EcoRII gene did not exhibit the full-length c opies of the gene. Lower methylation of CpNpG sequences characteristic of a ll transformed cells could result from the disturbance of one of several pl ant DNA methyltransferase genes following its homologous recombination with the M.EcoRII gene.