FIGURE 1.

The proposed long range RT pathway involves a conserved tyrosine residue in the C-terminal tail of class Ia RNR small subunit. A, the proposed long range RT pathway between the α₂ and β₂ subunits (only one α and one β are shown) of the E. coli class Ia RNR. An essential tyrosine in the RT pathway, Tyr³⁵⁶ in E. coli, corresponds to Tyr³⁷⁶ and Tyr³²³ in β and β′, respectively. B, sequence alignment of the C-terminal tails of the RNR small subunits from E. coli (NrdB) and S. cerevisiae (Rnr2(β) and RNR4(β′)).