Most of the nucleic acid contents and nucleic acid binding proteins can be eliminated by the addition of streptomycin (sulphate) to the supernatant. The final concentration of streptomycin sulphate may vary from 0.6 to 1% depending on the experiment and the sample must be stirred. Finally, the precipitate is removed by centrifugation (12,000 rpm for 15 to 20 mins).
Also, kindly avoid multiple freeze thaw cycles during sample storage prior to protein purification which is likely to cause cell lysis and increase the viscosity of the supernatant.