IN-VIVO AGGREGATION OF MAIZE ACTIVATOR (AC) TRANSPOSASE IN NUCLEI OF MAIZE ENDOSPERM AND PETUNIA PROTOPLASTS

The transposase (TPase) of the maize transposon Activator (Ac) accumul ates in the nuclei of maize endosperm and transfected Petunia protopla sts, where it aggregates into rod-like structures about 2 mu m in leng th. In petunia protoplasts the amount of TPase aggregates increases wi th the strength of the promoter fused to the Ac-coding region. The exc ision frequency of a Ds element, however, does not increase proportion ally. The data suggest that the aggregated TPase is not responsible fo r the mobilization of the Ds element, but rather is a transpositionall y inactive form of the protein. In contrast to the full-length TPase, a functional, N-terminally truncated TPase derivative is inefficiently transported into the nucleus at high expression levels and aggregates predominantly in the cytoplasm. Accordingly, the N-terminus of the TP ase is involved in nuclear localization and/or aggregation.