Catalyzes the transfer of one adenosine molecule from an ATP to an mRNA poly(A) tail bearing a 3'-OH terminal group and enhances mRNA stability and gene expression (PubMed:34048638). Can also elongate RNA oligos ending with uridine molecule, provided that the sequence is adenosine-rich (By similarity). Mainly targets mRNAs encoding endoplasmic reticulum-targeted protein (PubMed:28931820). ATP + RNA(n) = diphosphate + RNA(n)-3'-adenine ribonucleotide Interacts with BCCIP and PABPC1; the interaction has no effect on TENT5C poly(A) polymerase function. Interacts with PLK4; this interaction leads to the TENT5C recruitment into the centrosome. Recruited into the centrosome through its interaction with PLK4. Expressed by splenocytes, expression is increased in activated splenocytes. In splenocytes, expression is highly induced after yctivation by IL4 and LPS. Animals do not display major developmental phenotypes. They suffer from anemia with lower hemoglobin levels compared to controls. They have increased proliferation of B cells. Belongs to the TENT family. Extended N-terminus. Extended N-terminus.