Incubation of nuclei and chromatin isolated from guinea pig spleen (bu
t not thymus or liver) at 37 degrees C for 1 h induces proteolysis of
histones H1 and H2A and generates specific products. Electrophoresis w
ith sodium dodecyl sulfate reveals a decrease in contents of histones
H1 and H2A, anti the appearance of proteins traveling ahead of histone
H1(0) and between histones H2A and H4. Addition of to mM ATP (but nor
cAMP or PPi) to the reaction mixture prevents cleavage of histones H1
and H2A and the appearance of the above described proteins. ATP prote
cts the nuclear and chromatin histones from proteinases and promotes d
egradation of low-molecular-weight cytosol proteins. The mechanisms of
structural modifications of chromatin by ATP causing the nuclear prot
eins to resist proteolysis are discussed.