Both an altered DNA structure and cellular proteins are involved in protecting a triplex forming an oligopurine-rich sequence from Dam methylation in E. coli.
When the 4-bp Dam recognition sequence was placed between two d(GA)7 tracts, it became severely undermethylated in JM101 Escherichia coli cells compared to other Dam sequences in the same plasmid DNA. This site specific undermethylation was also detected on supercoiled molecules in vitro. Mutational analysis indicated that undermethylation is related to the capacity of the oligopurine tract to adopt the H-DNA conformation. In addition, chemical probing of the cells was consistent with a cellular protein bound to the DNA. Therefore it is likely that the combination of altered DNA conformation and a cellular protein leads to Dam-site protection. We also found that the site-specific undermethylation is detectable in certain E. coli strains only.
Klysik
J
J
Institute of Biosciences and Technology, Texas A&M University, Texas Medical Center, Houston 77030, USA.
D001426:Bacterial Proteins / Q000378:metabolism*; D001483:Base Sequence; D001665:Binding Sites; D018983:DNA Footprinting; D019175:DNA Methylation; D004269:DNA, Bacterial / Q000737:chemistry / Q000378:metabolism*; D004277:DNA, Single-Stranded / Q000378:metabolism; D004278:DNA, Superhelical / Q000378:metabolism; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism*; D029968:Escherichia coli Proteins; D008969:Molecular Sequence Data; D009690:Nucleic Acid Conformation; D009838:Oligodeoxyribonucleotides; D011687:Purines; D015265:Site-Specific DNA-Methyltransferase (Adenine-Specific) / Q000378:metabolism*; D013329:Structure-Activity Relationship
D001426:Bacterial Proteins; D004269:DNA, Bacterial; D004277:DNA, Single-Stranded; D004278:DNA, Superhelical; D029968:Escherichia coli Proteins; D009838:Oligodeoxyribonucleotides; D011687:Purines; C058693:Dam methyltransferase; D015265:Site-Specific DNA-Methyltransferase (Adenine-Specific); C499294:dam protein, E coli; C030985:purine