Synchronization of DNA synthesis in Neurospora crassa by 2'-deoxyadenosine and spore selection.

2'-Deoxyadenosine (2 mM), a DNA inhibitor, was used to synchronize DNA synthesis in cultures of Neurospora crassa lys 3. The cultures recovered spontaneously from the inhibitor which had little or no effect o the synthesis of RNA, protein or carbohydrate or on the specific growth rate of the mould. The degree of 'synchrony' of DNA synthesis obtained with 2'-deoxyadenosine varied directly with the organism's specific growth rate when the latter was altered by temperature changes. A direct relationship was observed between the rate of synthesis of DNA during the S period and the organism's specific growth rate. Conidia of Neurospora crassa lys 3 were separated into different density classes using urografin gradients; the separation treatment did not have an appreciable effect on the subsequent germination or growth of conidia. Populations of large, less dense conidia produced germ tubes more rapidly and more synchronously than populations of small, dense conidia. Cultures inoculated with the large conidia displayed continuous synthesis of RNA and protein but discontinuous synthesis of DNA.