A ribonuclease, RNase T-tat, specifically designed to hydrolyze the TAR RNA of HIV-1 virus has been engineered. The protein was made by domain swapping the TAT peptide at the loop 3 position of ribonuclease T1. The RNase T-tat maintains a guanine-specific RNA hydrolytic activity, and characteristically displayed a specific affinity for the TAR RNA of HIV-1. In the in vitro and in vivo assays, the RNase T-tat preferentially inhibited the expression of TAR-bearing mRNA through cis-TAR targeting, suggesting that RNase T-tat may be potentially useful for the disruption of the initial stage of the transcription process of HIV-1 virus.