cell the concentration of flu xaatat peptide stock solutions was determined in ph 9 buffer 1 mm sodium phosphate 1 mm sodium citrate and 1 mm sodium borate based on the absorbance of 6 carboxyfluorescein u03b5 492 81000 the uv absorbance was collected at 492 nm over 1 minute 60 u00d7 1 sec to accurately determine the concentration of the sample based on the beer lambert law the concentration of the peptide solutions was derived using kaleidagraph 3 52 synergy software ca the binding affinity of xaatat peptides xaa agh arg and agb for tar rna was measured by fluorescence anisotropy using a varian cary eclipse fluorescence spectrophotometer the anisotropy r was calculated using the following equation where i vv i vh i hh i hv are the fluorescence intensities with the excitation polarizer and emission polarizer is oriented perpendicular i vh and i hv and parallel i vv and i hh to the direction of the polarized excitation the fluorescein labeled tar rna f tar rna was excited at 490 nm and the polarized emissions were monitored at 512 nm the slits were set at 10 nm for both excitation and emission the integration time was 20 seconds all data were measured in a sub micro starna cell inc with a starting volume of 160 u03bcl each addition 1 u03bcl of xaatat was equilibrated for two minutes before the fluorescence signal was recorded all experiments were performed at room temperature in tkt buffer tkt 50 mm tris hcl ph 7 4 20 mm kcl and 0 02 tween20 the initial concentration of f tar rna was 25 nm the tkt solution and peptide stock solution were both equilibrated at room temperature more than 20 minutes before the experiment the experiment was repeated three times.