SIMIAN VIRUS-40 LARGE T-ANTIGEN ISOELECTRIC FOCUSES AS MULTIPLE SPECIES WITH VARYING PHOSPHATE CONTENT

Simian Virus 40 large T antigen (TAg), radiolabeled with [32P]orthophosphate and with/without [3H]methionine, was found to isoelectric focus as four distinct species distributed in a highly reproducible pattern. These species have been found to differ in their 32P 3H ratios indicating that individual monomers of large TAg are heterogeneous in their phosphate content and suggesting, further, that large TAg may be differentially phosphorylated in vivo. Also, by increasing the concentration of large TAg the more basic species can be displaced into the more acidic species suggesting that the different isoelectric focusing forms represent aggregates of large TAg with varying phosphate content. © 1979.