Sources of nitrogen atoms and regulation of nucleotide and polyamine biosynthesis. PRPP, phosphoribosyl pyrophosphate; PRPS2, phosphoribosyl pyrophosphate synthetase 2; CAD, carbamoyl-phosphate synthetase 2; Gln, glutamine, Glu, glutamate; Gly, glycine; Asp, aspartate; Fum, fumarate; IMPDH1/2, inosine-5-monophosphate dehydrogenase; TS, thymidylate synthase; GMPS, guanosine monophosphate synthetase; DCK, deoxycytidine kinase; TK, thymidine kinase, ARG1, arginase 1; ODC, ornithine decarboxylase; CAT1/2, cationic amino acid transporter.