Schematics of a pyrimidine salvage pathway. Model of deoxyribose nucleotide salvage pathway. Double dashed line indicates block in a pathway due to gene deletion or in case of pathway 9 (dUMP → dTMP), block in pathway due to starvation of cells for essential cofactor tetrahydrofolate (not shown) by TMP treatment. Thymine and thymidine represent external metabolites transported from the media. Genes associated with pathways: 1 - cdd; 2 - deoA; 3 - deoB; 4 - deoC; 5 - tdk; 6 - yjjG; 7 - tdk; 8 - nudI/dut; 9 - thyA; 10 - tmk; 11 - ndk. Abbreviations: dCyt: deoxycytidine; dUrd.: deoxyuridine; Ura. - uracil; dR1P - deoxyribose-1-phosphate; dR5P: deoxyribose-5-phosphate; G3P/acet.: glyceraldehyde-3-phophate/acetaldehyde; Thd - thymidine (external); Thy - thymine (external).