The carboxy-terminus of the Ac transposase can activate gene expression in S. cerevisiae
--Essers, L and Kunze, R

In the course of our two-hybrid studies to localize the Ac transposase interaction domain (see above) we detected a transcription activation function in yeast of the C-terminal 24 residues. A fusion of this transposase segment to the C-terminus of the GAL4 DNA-binding domain results in a weak, but significant transcriptional activation of the lacZ gene in the absence of the GAL4 activation domain. This activity is lost if approximately 100 amino acids are removed from the C-terminus of the TPase derivatives. Interestingly, this activation activity is only detectable if more than 300 amino acids are deleted from the N-terminus of the transposase. We therefore assume that in longer hybrid transposase proteins either the fused GAL4 DNA-binding domain or the N-terminal transposase moiety itself masks the activation function by steric hindrance. However, the C-terminus of the Ac TPase has a very hydrophilic character and thus is probably located on the surface of the protein. As the transposase protein binds closely upstream of the Ac promoter, it is tempting to speculate that it could have a positive autoregulatory activity. However, it remains to be determined if transcriptional activation by the Ac transposase is also occurring in plants or if it is rather a coincidental phenomenon in yeast.
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