Histones and DNA methylation in mammalian chromatin. II. Presence of non-inhibitory tightly-bound histones.
After removal, by high-salt extraction, of the loosely-bound components present in human placenta chromatin, tightly-bound cationic proteins could be solubilized, by acid extraction, from the 'stripped' chromatin, as well as from the 'stripped' loops or from the 'digested matrix'. These acid-soluble tightly-bound proteins are, in terms of apparent molecular mass and immunoreactivity, quite similar to the 'typical', loosely-bound histones, and, similarly to their 'loosely-bound' counterparts, they can be subdivided in distinct H1-, H2A-, H2B-, H3- and H4-like components, the 'digested matrix' being however characterized by the absence of tightly-bound H1. These tightly-bound histones, at variance from the 'typical' ones, readily find a right-handed helical conformation upon renaturation by progressive dialyses. The H1 components strongly differ also in their effects on enzymic DNA methylation: while 'typical' H1 has a strong inhibitory effect, its tightly-bound counterpart exerts a slight but definite stimulation.
Caiafa
P
P
Department of Biochemical Sciences, University of Rome La Sapienza, Italy.
Reale
A
A
D'Erme
M
M
Allegra
P
P
Santoro
R
R
Strom
R
R
D002843:Chromatin / Q000737:chemistry / Q000378:metabolism*; D002942:Circular Dichroism; D015254:DNA Modification Methylases / Q000378:metabolism*; D006657:Histones / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D006801:Humans; D008745:Methylation; D009690:Nucleic Acid Conformation; D013056:Spectrophotometry, Ultraviolet
D002843:Chromatin; D006657:Histones; D015254:DNA Modification Methylases