PURIFICATION AND CHARACTERIZATION OF THE CYTOPLASMIC HISTONE ACETYLTRANSFERASE-B OF MAIZE EMBRYOS

From a soluble cellular fraction of maize embryos we purified to appar ent homogeneity a cytoplasmic histone acetyltransferase, which matches all criteria for a B-type enzyme, Using 8 chromatographic steps, we a chieved a 6700-fold purification of an enzymatically active protein wi th a molecular weight of similar to 90 kDa, Under denaturing condition s the protein split into 2 components which migrated at 45 and 50 kDa in SDS-PAGE, suggesting that the native enzyme is a heterodimer, The p urified enzyme was characterized in terms of physicochemical and kinet ic properties, and substrate specificity, It was specific for histone H4, leading to acetylation of non-acetylated H4 subspecies into the di -acetylated state in vitro. Its activity was coincident with the inten sity of DNA replication in meristematic cells during embryo germinatio n, We established an electrophoretic system under non-denaturing condi tions for detection of enzyme activity within the gel matrix; in combi nation with second dimension SDS-PAGE the procedure allowed the unambi guous identification of histone acetyltransferase, even in crude enzym e preparations.