Regulation of fungal ribonucleotide reductase by unusual dinucleotides

Three phosphorylated dinucleosides designated HS1, HS2, and HS3, isolated from the water-mould Achlya , were shown to significantly inhibit ribonucleotide reductase activity from Achlya . All three compounds decreased CDP reduction in fungal extracts by 50% at concentrations of 0.1mM. At the same concentration HS3 also inhibited partially purified CDP reductase from Chinese hamster ovary cells by at least 80% but showed only 10% inhibition with enzyme from E. coli . ADP reductase activity from Achlya was inhibited 50% by both HS1 and HS3 at 0.1mM. HS2 however, showed no inhibitory effect on purine reduction. The levels of ribonucleotide reductase during the asexual growth cycle of Achlya correlated with thymidine uptake into DNA and with the synthesis of HS compounds.