Formylates methionyl-tRNA in mitochondria and the cytoplasm. Responsible for the formylation of the 8 N-terminally formylated (Nt-formylated) mitochondrial matrix proteins that are encoded by mitochondrial DNA. Nt-formylated proteins in the cytoplasm are strongly up-regulated in stationary phase or upon starvation for specific amino acids (His or Lys) and are targeted for degradation by a PSH1 E3 ubiquitin ligase-mediated fMet/N-end rule pathway. Increased Nt-formylation of cytosolic proteins appears to be important for adaptation to these stresses. Stationary phase-degraded Nt-formylated proteins include histone H3-like centromeric protein CSE4, Mediator complex subunit 3 (PGD1) and small ribosomal subunit protein uS8-A (RPS22A)