A, Immunoblot from cell lysates of Jurkat cells or SHMT2-null Jurkat cell lines clones expressing an SHMT2 cDNA under the control of a doxycycline-inducible promoter (DOXi SHMT2), for proteins encoded by the indicated genes. Doxycycline was added at the indicated concentrations for the indicated number of days. For the SHMT2 immunoblot, the arrow indicates the band corresponding to SHMT2 protein, whereas the larger band (*) is non-specific and visible at the exposure shown. B, Immunoblot as in A. Doxycycline was added at the indicated concentration for 3 days and then withdrawn for the indicated number of days. C, Immunoblots from cell lysates of Jurkat cells expressing shRNAs targeting SHMT2 with or without expression of a codon-optimized, shRNA-resistant SHMT2 cDNA (SHMT2res).