One of three nuclear localization signals of maize Activator ( Ac ) transposase overlaps the DNA‐binding domain

Abstract

The nuclear localization sequences (NLSs) of the Ac transposase (TPase) protein have been characterized by indirect immunofluorescence detection of TPase deletion derivatives and TPase/β‐glucuronidase (GUS) fusion proteins in transiently transfected Petunia cells. The TPase contains 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 TPase. NLS(44–62) and NLS(159–178) are bipartite NLSs, whereas the structure of NLS(174–206) does not allow a classification into one of the three major NLS categories. NLS(174–206) overlaps with the basic DNA‐binding domain of TPase. A substitution of two amino acids in this segment (HiS 191 →Arg and Arg 193 →His) results in a total loss of DNA‐binding activity, but retains reduced NLS activity. Accordingly, the two functions can be separated. In addition, we show that a NLS‐deficient 71 kDa TPase derivative is co‐imported into the nucleus in the presence of wildtype TPase.