ANALYSIS OF NONMETHYLATED GATC SITES IN THE ESCHERICHIA-COLI CHROMOSOME AND IDENTIFICATION OF SITES THAT ARE DIFFERENTIALLY METHYLATED IN RESPONSE TO ENVIRONMENTAL STIMULI

Seven GATC sites that are nonmethylated in logarithmic growth phase ce lls using glycerol as a carbon source were isolated from the Escherich ia call chromosome. Three of these GATC sites are located upstream of the operons gut, mtl, and ppiA, whereas DNA sequences adjacent to thre e other nonmethylated GATC sites are not homologous to previously iden tified genes. The seventh nonmethylated GATC site is located downstrea m of uspA. The protection of this site from DNA methylation requires l eucine-responsive regulatory protein and is leucine responsive. The ca rbon source and the grow,th phase influenced the protection of the GAT C site 5' of the ppiA gene. The other five sites were protected under all the environmental conditions examined.