ONE OF 3 NUCLEAR-LOCALIZATION SIGNALS OF MAIZE ACTIVATOR (AC) TRANSPOSASE OVERLAPS THE DNA-BINDING DOMAIN

The nuclear localization sequences (NLSs) of the Ac transposase (TPase ) protein have been characterized by indirect immunofluorescence detec tion of TPase deletion derivatives and TPase/beta-glucuronidase (GUS) fusion proteins in transiently transfected Petunia cells. The TPase co ntains three NLSs near its amino-terminal end, NLS(44-62), NLS(159-178 ) and NLS(174-206), each of which is sufficient to redirect GUS to the nucleus. Deletion of the N-terminal 102 TPase residues including NLS( 44-62) results in strongly reduced nuclear import of the truncated TPa se. NLS(44-62) and NLS(159-178) are bipartite NLSs, whereas the struct ure of NLS(174-206) does not allow a classification into one of the th ree major NLS categories. NLS(174-206) overlaps with the basic DNA-bin ding domain of TPase. A substitution of two amino acids in this segmen t (His(191)-->Arg and Arg(193)-->His) results in a total loss of DNA-b inding activity, but retains reduced NLS activity. Accordingly, the tw o functions can be separated. In addition, we show that a NLS-deficien t 71 kDa TPase derivative is co-imported into the nucleus in the prese nce of wild-type TPase.