 The regulation of RNR and related enzymes maintains a balance of dNTPs relative to each other and relative to NTPs in the cell . Very low dNTP concentration inhibits DNA synthesis and DNA repair and is lethal to the cell , while an abnormal ratio of dNTPs is mutagenic due to the increased likelihood of the DNA polymerase incorporating the wrong dNTP during DNA synthesis . Regulation of or differential specificity of RNR has been proposed as a mechanism for alterations in the relative sizes of intracellular dNTP pools under cellular stress such as hypoxia . 
