FIGURE 4.

Comparison of growth phenotypes of β(Y376F) and β′(Y323F) mutants lacking the conserved tyrosine residue in their C-terminal tails. A, the β-Tyr³⁷⁶ residue is required for mitotic growth. RNR2 shuffle strains (Δrnr2, URA3CENRNR2) harboring a CENLEU2 vector expressing WT-RNR2 or the rnr2(Y376F) mutant were streaked onto a SC-Leu plate containing 5-FOA to eject the URA3 plasmid. Growth on the 5-FOA plate indicates that the copy of RNR2 on the CENLEU2 plasmid can provide the essential RNR2 function for mitotic survival. B, Western blots show comparable levels of the wild-type ^MycRnr2 and ^MycRnr2(Y376F) mutant proteins expressed in the RNR2 shuffle strain before 5-FOA selection. C, the β′-Tyr³²³ is not required for mitotic growth. Serial dilutions (1:10, starting from 1 × 10⁶ cells) of the RNR4 shuffle strain (Δrnr4, URA3CENRNR4) harboring a CENHIS3 vector expressing the wild-type RNR4 or the rnr4(Y323F) mutant were plated on a SC-His plate containing 5-FOA to eject the URA3 plasmid. The plate was photographed after 3 days of incubation at 30 °C.