Studies of the Putative Transforming Protein of the Type I Human T-Cell Leukemia Virus

The putative transforming protein of the type I human T-cell leukemia virus (HTLV-I) is a 40-kilodalton protein encoded by the X region and is termed p40$^{\text{xI}}$. On the basis of both subcellular fractionation techniques and immunocyto-chemical analysis, it is now shown that p40$^{\text{xI}}$ is a nuclear protein with a relatively short half-life (120 minutes). It is synthesized de novo in considerable quantities in a human T-cell line infected with and transformed by the virus in vitro, and it is not packaged in detectable amounts in the extracellular virus.