Red blood cell development is a unique process where reduced transcriptome and proteome complexity facilitates vast hemoglobin production. Here, we describe the cooperative role of cytoplasmic poly(A) polymerase TENT5C and the poly(A) tail-protecting LARP4/5 RNA-binding proteins in ensuring proper hemoglobin production. TENT5C catalytic mutant knock-in mice display microcytic hypochromic anemia resembling constitutive knockout. TENT5C counteracts gradual globin mRNA deadenylation during erythropoiesis. In the late stages, TENT5C dysfunction leads to globin poly(A) tail shortening and a drastic reduction of mRNA levels in reticulocytes. Proteomic experiments revealed transient but specific association of TENT5C with LARP4/5. Indeed, LARP4/5 depletion leads to downregulation and poly(A) tail shortening of globin mRNAs. Furthermore, lack of TENT5C catalytic activity is accompanied by compensatory upregulation of LARP4/5. Finally, the importance of precise regulation of globin poly(A) tails by deadenylation and re-adenylation is highlighted by the destabilization of TENT5C by CCR4-NOT deadenylase complex-associated E3 ubiquitin ligase CNOT4. This repository contains supplementary data accompanying related publication. The uploaded files contain following data: Supplementary Data 1 DRS of E14.5 fetal livers, poly(A) profiling statistics. Supplementary Data 2 (A) All identified proteins in the TurboID assay (B) Overlap between 3 replicates (C) Statistically significant GO terms for overlapping proteins with average specificity > 0. Supplementary Data 3 (A) Overview of used input and method details used in degronopedia analysis (B) Identified degron motifs (C) Degron conservation (D) Evolutionary conservation of TENT5C aa sequence scored by ConSurf (The table shows the residue variety in % for each position in the query sequence, each column shows the % for that amino acid found in position in the MSA). Supplementary Data 4 Key resources table. Supplementary Data 5 Oligonucleotides used in the study. Supplementary Resource 1 TurboID assay MS/MS raw data, each file in the archive corresponds to a biological replicate of either WT (control) or Tent5c-EGFP.