TCP10L, a transcriptional repression factor gene that was localized on human chromosome 21q22.11, was identified to be derived through segmental duplication since the divergence of primates and rodents. It was elucidated that TCP10L gene was a primate-specific gene in this study. Subsequently it was demonstrated that the putative leucine zipper motif mediated the homodimerization of TCP10L. Using in vitro and in vivo methodologies, it was shown that either deletion or point mutation of the leucine zipper motif was sufficient to abolish TCP10L homodimerization. In Hela cells, both the exogenous wild type TCP10L and endogenous TCP10L were detected on nuclei with immunofluorescence assay. However, the leucine zipper motif mutants of TCP10L could also be detected on nuclei. The results suggested that the leucine zipper motif enabled TCP10L to homodimerize, but was not essential for the TCP10L nuclear localization.