THE PROTEIN EFFECT ON DETERMINATION OF DNA WITH HOECHST-33258

The present study was designed to afford a critical review of the effe ct of proteins on the Hoechst 33258 method for determination of DNA of crude homogenates. A considerable effect of proteins on the fluoresce nce was observed when the concentration exceeded 100 mu g BSA equivale nt protein. Below that value, practically no effect of proteins was no ted. We used proteinase K to remove the proteins, but dilution of homo genates could be used as well. Moreover, we found that the concentrati on of the fluorochrome should be between 1 mu g and 2 mu g when microg ram levels DNA are to be determined.