Sulfhydryl reagents prevent dephosphorylation and proteolysis of histones in isolated HeLa metaphase chromosomes.

It has been shown by D'Anna et al. [Nucleic Acids Res. 5, 3195-3207 (1978)] that histones H1 and H3, which are highly phosphorylated during mitosis in mammalian cells, become rapidly dephosphorylated during conventional metaphase chromosome isolation procedures. We show here that this dephosphorylation can be completely prevented by including sulfhydryl reagents, such as p-chloromercuriphenyl sulfonate or 5,5'-dithiobis(2-nitrobenzoate), in the chromosome isolation buffers. These reagents also efficiently inhibit the endogenous proteases present in isolated HeLa chromosomes and nuclei.