Do tightly-bound chromatin proteins play a role in DNA methylation?
When chromatin matrix, "stripped" from its loosely-bound components by extraction with 3 M NaCl, is extensively digested with DNAase I, a fraction is obtained, which carries no endogenous DNA methyltransferase activity but which is a good substrate for externally added enzyme. Under the same conditions, protein-free DNA isolated from this fraction can instead hardly be methylated, this different behaviour pointing to a role of DNA-tightly-bound proteins in favoring or promoting the catalytic action of the enzyme. A similar stimulation of enzymatic methylation could also be shown when, in the presence of this same fraction, single stranded Micrococcus luteus DNA was incubated with placental methyltransferase, using S-adenosylmethionine as a methyl donor. This finding can be correlated to the existence, in chromatin loops, of small regions which resist digestion by DNAase I also after high-salt removal of their loosely-bound components (presumably because of the presence of tightly-bound proteins) and whose DNA is characterized by high methylation levels and, at the same time, by high relative content of thymine.
Caiafa
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P
Dipartimenti di Scienze Biochimiche, Università di Roma La Saplenza, Italy.
Mastrantonio
S
S
Attina
M
M
Rispoli
M
M
Reale
A
A
Strom
R
R
D001665:Binding Sites; D002384:Catalysis; D002843:Chromatin / Q000302:isolation & purification* / Q000502:physiology; D002851:Chromatography, High Pressure Liquid; D004247:DNA / Q000302:isolation & purification*; D015254:DNA Modification Methylases / Q000302:isolation & purification; D004268:DNA-Binding Proteins / Q000302:isolation & purification* / Q000502:physiology; D003850:Deoxyribonuclease I; D005260:Female; D008401:Gas Chromatography-Mass Spectrometry; D006801:Humans; D006868:Hydrolysis; D066298:In Vitro Techniques; D008745:Methylation; D010920:Placenta / Q000201:enzymology / Q000378:metabolism; D011247:Pregnancy
D002843:Chromatin; D004268:DNA-Binding Proteins; D004247:DNA; D015254:DNA Modification Methylases; D003850:Deoxyribonuclease I