Effect of procedures for the reduction of the nucleic acid content of SCP on the DNA content of Saccharomyces cerevisiae

Autolysis of a suspension of baker's yeast, triggered by heat shock, organic solvents or drying/rehydration, had previously been found to degrade yeast RNA to diffusible products, leaving a resistant, cell‐bound fraction characterised by a high adenine: guanine ratio, which it was suggested might be DNA. Analysis for DNA by the diphenylamine reaction now shows that even when autolysis (following heat shock) is prolonged to the point at which the cells lose 42% of dry matter and half their protein content, no DNA leaves the cells. Overnight treatment of freeze‐dried yeast preparations with In perchloric acid at room temperature extracts the purines of DNA in the free form, and estimations of DNA content based on this agree with the results of the diphenylamine method in the case of autolysed or alkaline salt‐extracted yeast preparations, which have a low RNA content. With untreated yeast, which contains 20 times as much RNA as it does DNA, the picture is complicated by a slow, but significant depurination of RNA by 1N perchloric acid. The implications of this, and other findings, are considered in respect of analytical procedures for yeast DNA and RNA content.