Polynucleotide kinase that can phosphorylate the 5'-hydroxyl groups of double-stranded RNA (dsRNA), single-stranded RNA (ssRNA), double-stranded DNA (dsDNA) and double-stranded DNA:RNA hybrids. dsRNA is phosphorylated more efficiently than dsDNA, and the RNA component of a DNA:RNA hybrid is phosphorylated more efficiently than the DNA component. Plays a key role in both tRNA splicing and mRNA 3'-end formation. Component of the tRNA splicing endonuclease complex: phosphorylates the 5'-terminus of the tRNA 3'-exon during tRNA splicing; this phosphorylation event is a prerequisite for the subsequent ligation of the two exon halves and the production of a mature tRNA (PubMed:24766809, PubMed:24766810). Its role in tRNA splicing and maturation is required for cerebellar development (PubMed:24766809, PubMed:24766810). Component of the pre-mRNA cleavage complex II (CF-II), which seems to be required for mRNA 3'-end formation. Also phosphorylates the 5'-terminus of exogenously introduced short interfering RNAs (siRNAs), which is a necessary prerequisite for their incorporation into the RNA-induced silencing complex (RISC). However, endogenous siRNAs and microRNAs (miRNAs) that are produced by the cleavage of dsRNA precursors by DICER1 already contain a 5'-phosphate group, so this protein may be dispensible for normal RNA-mediated gene silencing. a 5'-end dephospho-2'-deoxyribonucleoside-DNA + ATP = a 5'-end 5'-monophospho-2'-deoxyribonucleoside-DNA + ADP + H(+) a 5'-end dephospho-ribonucleoside-RNA + ATP = a 5'-end 5'-monophospho-ribonucleoside-RNA + ADP + H(+) Component of the tRNA splicing endonuclease complex, composed of CLP1, TSEN2, TSEN15, TSEN34 and TSEN54 (PubMed:24766809). Component of pre-mRNA cleavage complex II (CF-II). Also associates with numerous components of the pre-mRNA cleavage complex I (CF-I/CFIm), including NUDT21, CPSF2, CPSF3, CPSF6 and CPSF7. Interacts with CSTF2 and SYMPK. The disease is caused by variants affecting the gene represented in this entry. Neurodegeneration is due to defects in tRNA splicing (PubMed:24766809, PubMed:24766810). Belongs to the Clp1 family. Clp1 subfamily.