Abstract: Tree shrew (Tupaia belangeri) is not infected by HIV-1,and its cells apparently support postentry events in HIV-1 infection.Cyclin T1 binding with HIV-1 Tat is responsible for HIV-1 transcription.To understand whether tree shrew cyclin T1 (tsCycT1) binds with HIV-1 Tat protein,the designed primers and RT-PCR were used to amplify the tsCycT1 cDNA.The clone of full-length tsCycT1 cDNA is of 2 175 bp.The homology of tsCycT1 with that of human CycT1 (hCycT1) is 92.6% at nucleotide level and 94.1% at deduced amino acid level,respectively.The first 272 amino acids have 98.8% of homology with hCycT1,and the residue at position C261 is the cysteine.These results suggest that tsCycT1 can form a high-affinity and zinc-dependent complex binding to HIV-1 Tat and TAR,which may support HIV-1 transcription.