A translational inhibitor from muscles of diabetic rats: identification as histone H1

A heat- and acid-stable protein fraction that inhibited peptide chain initiation in rabbit reticulocyte lysates was extracted from frozen, powdered rat skeletal muscles by stepwise trichloroacetic acid precipitation. Streptozotocin-induced diabetes increased the inhibitory activity; this was prevented by insulin therapy. Size-exclusion high-performance liquid chromatography resolved four inhibitory fractions; only one was consistently increased (approximately 2-fold) in muscle extracts from diabetic rats. Polysome profiles of lysates incubated with this fraction indicated peptide chain initiation inhibition. On sodium dodecyl sulfate-polyacrylamide gel electrophoresis the purified inhibitory fraction migrated with apparent Mr 30 and 32 kDa, which on Western blot immunostained with antisera against histone H1/H1(0). Perchloric acid extraction of muscle homogenates yielded approximately twofold more H1 from diabetic than from control rats; yield from diabetics decreased to control values 5 h after subcutaneous insulin injection. Inclusion of detergent during homogenization increased H1 yield more from muscles of control than from diabetic rats and abolished the difference between them. Because H1 affects several biochemical reactions, its facilitated extraction from insulin-deprived tissues can bias interpretation of studies of insulin action.