We have continued our studies on the Ac protein. We detect a specific reaction in Western blots with a protein (apparent molecular weight of 110 kD) with two antisera prepared against fusion proteins containing separate segments from the long ORF of Ac in E. coli. We detect the same protein in Spodoptera frugiperda cells infected with a Baculovirus vector containing a cDNA copy of the Ac-coding region. In the insect cells, the protein is 500-1000 times more abundant than in maize cells. Degradation of the protein leads to a pattern of peptides reacting with our antisera. Those degradation bands visible in the maize extracts can also be seen in the degradation pattern in the protein from the insect cells. This supports the hypothesis that the reactive protein in maize cells that is found in nuclei from Ac-carrying, but not from Ac-free cells, is indeed the Ac protein.

The predicted molecular weight of this protein is only 92,000. However, it is known that other nuclear proteins also migrate more slowly than expected on the basis of their predicted molecular weights.

Heidi Fusswinkel, Markus Miiller-Neumann, Charlotte Both, Walter Doerfler and Peter Starlinger

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