Terminal uridylyltransferase which is involved in the post-transcriptional editing of mitochondrial RNA, a process involving the addition and deletion of uridine (U) nucleotides in the pre-RNA (PubMed:11893335, PubMed:20086102, PubMed:26833087, PubMed:27744351). Specifically, catalyzes the addition of Us to the 3'-hydroxyl group of guided RNA (gRNA), ribosomal RNA (rRNA) and some mRNAs (PubMed:11893335, PubMed:20086102, PubMed:26833087, PubMed:27744351). As part of the mitochondrial 3' processome (MPsome), catalyzes the primary 3' uridylation of gRNA precursors to facilitate their recognition and to induce their processive 3'-5' degradation by DSS1, and the secondary 3' uridylation of mature gRNAs (PubMed:26833087). Involved in the 3' uridylylation of the long A/U tail of some edited and never-edited mRNAs (PubMed:20086102). Promotes 3' uridylylation-mediated decay of some never-edited mRNAs (PubMed:20086102). Does not mediate RNA-independent UTP polymerization (PubMed:27744351). RNA(n) + UTP = diphosphate + RNA(n)-3'-uridine ribonucleotide Binds 1 Mg(2+) or Mn(2+) per subunit (PubMed:27744351). The type of divalent cation used by the enzyme affects the nucleotide specificity; Mg(2+) induces predominantly uridine (U) incorporation while Mn(2+) induces also substantial incorporation of both adenine (A) and cytosine (C) (By similarity). KM is 18-28 mM for UTP (at 27 degrees Celsius and 12 (U) single-stranded RNA as substrate) (PubMed:15304317). kcat is 100 min(-1) with UTP and 6(U) single-stranded RNA as substrates (PubMed:19465686). kcat is 0.0012 min(-1) with UTP and double-stranded RNA as substrates (PubMed:19465686). kcat is 15.5 min(-1) with UTP as substrate (PubMed:27744351). kcat is 23.5 min(-1) with RNA as substrate (PubMed:27744351). Oligomer (PubMed:27744351). Component of the mitochondrial 3' processome (MPsome) complex composed at least of terminal uridylyltransferase KRET1/TUT1, 3'-5' exonuclease DSS1, MPSS1, MPSS2 and MPSS3 (PubMed:26833087, PubMed:27744351). Within the complex, interacts with DSS1, MPSS1 and MPSS3 (PubMed:26833087). Expressed at the procyclic stage (at protein level). The C2H2-type zinc finger domain is required for the proper folding of the catalytic domain, but is dispensable for uridylation of single strand RNA substrate. RNAi-mediated knockdown at the procyclic stage causes severe growth defect and a severe reduction in mRNA editing (PubMed:11893335, PubMed:20086102, PubMed:26833087, PubMed:27744351). Reduced production of guided RNAs (gRNA) and rRNAs due to a block in the processing of gRNA and rRNA precursors (PubMed:20086102, PubMed:26833087). Accumulation of unprocessed precursors for some pre-edited and never-edited mRNAs (PubMed:20086102). Belongs to the DNA polymerase type-B-like family.