Biochemical properties of a transforming nonkaryophilic T antigen of SV40

We reconstructed into wt SV40 DNA a previously described deletion of the A gene, eliminating amino acids 110 through 152 of the large T (L. Fischer-Fantuzzi and C. Vesco (1985) Proc. Natl. Acad. Sci. USA 82, 1891-1895); the gene product of the new recombinant pACTSV2, like the previous product, has a cytoplasmic instead of a nuclear localization and efficiently transforms NIH3T3 cells. Three main functions of this nonkaryophilic large T (NKLT) were examined, and the results obtained were the following: the NKLT does not bind to the SV40 origin DNA under conditions where the normal large T shows specific binding; the NKLT has conserved the ability to form high molecular weight aggregates; the NKLT becomes phosphorylated in vivo at only two residues: serine 639 and threonine 701. This indicates that the NH2-terminal phosphorylation of the large T is unnecessary for established-cell transformation. In addition, this and previous evidence (K. H. Scheidtmann et al. (1984) J. Virol. 50, 636-640) suggest that the lack of phosphorylation in serines 106, 676, 677, and 679 may constitute a characteristic of the large T molecules with extranuclear localization.