Objective    To select the aptamer to an extracellular soluble fragment of recombinant human TGF-β receptor Ⅱ (TGF-β RⅡ) in order to antagonize TGF-β effectively by using systematic evolution of ligants by exponential enrichment (SELEX).     Methods    Initial random RNA library was transcripted in vitro from ssDNA 5′-TAATACGACTCACTATAGGGAGGACGATGCGG-N60-CAGACGACTCCCCGA-3′; rhTGF-β RⅡ was used as target protein. Totally

selection of 8 times was carried out in SELEX experiment. Membrane binding assay was performed to detect the evolution of enriched RNA library; Electrophoretic mobility shift assay (EMSA) was done to determine the affinity between the selected nucleic acid sequence and TGF-β RⅡ.     Results    Evolution of the enriched RNA library along the increased affinity to TGF-β RⅡ was observed with the development of selection. Two types of dominant sequences were isolated and named as sequence A and sequence B. In membrane binding assay

both sequences A and B showed obvious affinity to TGF-β RⅡ. However

no retarded bands were seen in EMSA.     Conclusion    The affinity of sequences A and B to TGF-β RⅡ is beyond satisfaction. However

possible sequences with improved affinity to TGF-β RⅡ can be selected by post-SELEX on the basis of candidate sequences A and B.