No. The fluorescent dyes (FAM, TAMRA and ROX) provided with the kits are activated as NHS (N-Hydroxy-Succinamide) esters. NHS esters are reactive with amines. Since Tris is an amine, it will react with the activated dye and act as a scavanger during the labeling reaction. This will reduce the efficiency of the labeling reaction. It is recommended that you exchange your protein into a PBS buffer prior to the labeling reaction using a Centri-Spin spin column (available from Princeton Separations) or related method based on gel filtration. The protein can be exchanged back into the Tris buffer following the labeling reaction.