Fig. 3. Analysis of the methylation state of carB exogenous and endogenous sequences in pMAT754 transformants. DNA of the wild-type stain R7B (WT) and albino (T6-T7) and wild-type (T10-T11) transformants was restricted with the isoschizomers MspI (M) and HpaII (H) (insensitive and sensitive to cytosine methylation, respectively), or with the enzyme ClaI, which is sensitive to cytosine methylation. Filter was hybridized with a 2.4 kb PstI–XhoI fragment of plasmid pMAT754, which contains the carB coding and promoter sequences. Arrows indicate fragments of 862 bp (HpaII–MspI digestion) and 888 bp (ClaI digestion), derived solely from endogenous carB sequences. Asterisks mark fragments exclusively derived from carB exogenous sequences. The sizes (in base pairs) of fragments of the 1 kb Plus ladder marker (Gibco-BRL) are indicated.