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ADP-ribosylated histone H1 was isolated from intact HeLa cells grown for 24 h with3H-adenosine and compared with ADP-ribosylated histone H1 synthesized from 3HNAD by isolated HeLa nuclei. Most (ADP-ribose)n-histone H1 conjugates formed in vivo carried single ADP-ribose units, less than one fourth of the total ADP-ribose residues being in the form of oligomeric or polymeric chains. (ADP-ribose)n linked to H1 in vivo was not released by neutral NH2OH to a significant extent. Alkali treatment (pH 10.5) liberated most but not all of the ADP-ribose residues which may indicate the existence of a new type of linkage so far found only in conjugates isolated from intact tissue. No ADP-ribosylated histone H1 complex of higher molecular weight ('H1 dimer') could be detected in intact cells. By contrast, isolated HeLa nuclei formed ADP-ribosylated histone H1 which contained predominantly polymeric ADP-ribose residues. The (ADP-ribose)n residues were linked by NH2OH-sensitive and by NH2OH-resistant, alkali (pH 10.5) labile bonds, the majority of the conjugates appearing in the form of the higher-molecular-weight complex. A comparison with the ADP-ribosylated non-histone proteins indicated that histone H1 formed in vivo carried less than 2.5% of the total protein-bound ADP-ribose residues and less than 1% of the protein-bound ADP-ribose synthesized in vitro.
Adamietz et al. (Wed,) studied this question.