Human methylated DNA-binding protein. Determinants of a pBR322 recognition site.
Methylated DNA-binding protein (MDBP) from human placenta has a high affinity for a site in pBR322 (pB site 1) when that site is methylated at its CpG dinucleotides. Dimethyl sulfate interference analysis and experiments with ligands prepared by oligonucleotide-directed mutagenesis indicate that 15 contiguous base pairs, 14 of which exhibit hyphenated dyad symmetry, influence MDBP binding to pB site 1. These 14 base pairs, 5'-RTMGYCAMGG(M/T)GAY-3' (M, 5-methylcytosine), suffice for recognition by MDBP as demonstrated with a double-stranded, MpG-containing oligonucleotide used as a free ligand or cloned into M13mp19 and subsequently methylated. Seven single-site mutations at different positions of this 14-base pair region largely eliminated binding, and several others increased binding up to 2-fold when compared to the nonmutant, triply methylated sequence. However, MDBP recognizes a site in hemimethylated M13mp19 replicative form DNA, which was homology to pB site 1 at only 10 of 14 base pairs, and all four of these different base pairs are equivalent to transversions. Based upon the above data, a mixed oligonucleotide probe was constructed that contains variants of pB site 1 which should be recognized by MDBP. This 14-base probe hybridizes under stringent conditions to a number of discrete fragments in restriction digests of human DNA. this suggests that there are multiple pB site 1-related sequences in human DNA that might, when methylated, bind MDBP in vivo.
Khan
R
R
Department of Biochemistry, Tulane Medical School, New Orleans, Louisiana 70112.
Zhang
X Y
XY
Supakar
P C
PC
Ehrlich
K C
KC
Ehrlich
M
M
D000595:Amino Acid Sequence; D001482:Base Composition; D001665:Binding Sites; D004247:DNA / Q000235:genetics; D004268:DNA-Binding Proteins / Q000378:metabolism*; D005260:Female; D006801:Humans; D008745:Methylation; D009154:Mutation; D010920:Placenta / Q000378:metabolism*; D010957:Plasmids; D011247:Pregnancy; D012689:Sequence Homology, Nucleic Acid; D013698:Templates, Genetic
D004268:DNA-Binding Proteins; D004247:DNA