Two sets of primers were designed according to the sequences of xynA and xynB from Aspergillus sulphureus, and the DNA fragments composed of 574 bp and 594 bp were amplified by polymerase chain reaction (PCR), respectively. The two PCR products respectively digested with EcoRⅠ/BamHⅠ and BglⅡ/HindⅢ were ligated into multiple cloning sites of pET-28a(+). The resulting plasmid is pET-xynAB, in which xylanase A and B are ligated by a 7-amino acid peptide (GlyGlyGlySerGlyGlyGly). E. coli BL21 transformed with pET-xynAB was induced by IPTG, and a special protein band about 50 ku was detected by SDS-PAGE. The protein purified with Ni-NTA column was denatured by 8 mol/L urea and dialyzed for refolding. The recombinant xylanase showed optimal activity at 50℃ and pH 4.4. The enzyme retained above 75% of its activity at the range of pH 2.4～5.4. The xylanase displayed about 50% retained acitivity after incubating at 80℃ for 30 min. Various metal ions have different effects on activity of the recombinant xylanase.

The regulator of expression of virion(Rev)protein binds specifically to the Rev-responsive element(RRE)RNA in order to regulate the expression of the human immunodeficiency virus(HIV)-1 genes.Fluores-cence indicator displacement assays have been used to identify ligands that can inhibit the Rev-RRE interaction;however,the small fluorescence indicators cannot fully replace the Rev peptide or protein.As a result,a single rhodamine B labeled Rev(RB-Rev)model peptide was utilized in this study to develop a direct and efficient Rev-RRE inhibitor screening model.Due to photon-induced electron transfer quenching of the tryptophan residue on the RB fluorophore,the fluorescence of RB in Rev was weakened and could be dramatically reactivated by interaction with RRE RNA in ammonium acetate buffer(approximately six times).The interaction could reduce the electron transfer between tryptophan and RB,and RRE could also increase RB fluorescence.The inhibitor screening model was evaluated using three known positive Rev-RRE inhibitors,namely,proflavin,6-chloro-9-[3-(2-chloroethylamino)pro-pylamino]-2-methoxyacridine(ICR 191),and neomycin,as well as a negative drug,arginine.With the addition of the positive drugs,the fluorescence of the Rev-RRE decreased,indicating the displacement of RB-Rev.This was confirmed using atomic force microscopy(AFM)and the fluorescence was essentially unaffected by the addition of arginine.The results demonstrated that RB-Rev can be used as a fluorescent probe for recognizing small ligands that target RRE RNA.The Rev-RRE inhibitor screening model offers a novel approach to evaluating and identifying long-acting Rev inhibitors.