A revival of interest has taken place in recent years in the possibility of interference with mam malian nucleic acid biosynthesis by means of an tagonists of the free pyrimidines. Early studies appeared to show that, while orotic acid (1, 48) and the sugar derivatives of the pyrimidines (19, 20) are extensively incorporated into both RNA and DNA, the incorporations of free uracil, cytosine, an...
