In employing PCR-select cDNA subtractive hybridization in our search for the etiologic agent of GTFP, we have amplified the turtle homologue of the tumor susceptibility gene TSG101, a recently discovered tumor susceptibility gene whose functional knockout in mouse fibroblasts leads to transformation and tumor formation in nude mice. Moreover, previous studies have indicated that over-expression of TSG101 antisense RNA causes transformation of naive 3T3 cells and elevation of stathmin mRNA, also known as oncoprotein 18, a cytoplasmic phosphoprotein elevated in a variety of malignancies and implicated in the regulation and relay of diverse signals associated with cell growth and differentiation. Analysis of the 1,176-bp full-length turtle TSG101 cDNA indicated sequence similarity of 82.3% and 84.4%, respectively, with the mouse and human TSG101 homologues. Also, alignment and comparison of the predicted 392-amino acid turtle TSG101 product showed a high degree of similarity with the human (91.9%) and mouse (89.3%) TSG101 proteins. A coiled-coil domain and a proline-rich region typical of activation domains of transcription factors were highly conserved among the reptilian and mammalian species. Moreover, the leucine zipper motif in the coiled-coil domains of the turtle, human and mouse TSG101 proteins were identical. Expression of the TSG101 gene was detected in various organs and cell lines from affected turtles. Attempts to determine the role of TSG101 in the pathogenesis of GTFP are currently underway.