Subcellular localization of DNA-binding protein BA by immunofluorescence and immunoelectron microscopy

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Abstract
Nonhistone protein BA decreases in amount in the chromatin of growth-stimulated normal rat liver and in mitogen[phytohemagglutinin]-stimulated normal human lymphocytes. Protein BA was purified and preferred to bind to double-stranded A-T [adenine-thymidine] rich DNA. Immunization of rabbits with highly purified protein BA resulted in the production of a specific antibody. A specific immunoreactivity for chromosomal protein BA was demonstrated by immunoelectrophoresis and double antibody immunoprecipitation analysis with rabbit anti-BA immunoglobulin [Ig] and IgG fractions. Light microscope examination of normal rat liver cryosections by the indirect immunofluorescence procedure demonstrated a cytoplasmic and nuclear localization for protein BA with a pronounced perinucleolar fluorescence. Immunoelectron microscopy employing the peroxidase antiperoxidase method of antigen localization confirmed the immunofluorescence data and showed a heterochromatin localization for protein BA. The relationship of the localization of protein BA to gene control in quiescent cells or to configurations of heterochromatin and the marked reduction in the amounts of protein BA which occur in stimulated growth states remains to be defined.