5-hmdU DNA kinase (HMUDK) and 5-hmdU DNA kinase 1 (HDMU1) are P-loop nucleotide kinases that phosphorylates 5-hydroxymethyluracil (5hmdU) into 5-phosphomethyl-2'-deoxyuridine (5-PmdU) on DNA as a step in the pathway leading to thymidine hypermodifications in the viral genome [2]. HMUDK also transfers glutamate to 5-pyrophosphoryloxymethyldeoxyuridine (5-PPmdU) to produce 5-Nalpha-glyutamylthymidine (Nalpha-GluT) [2,3]. These modifications probably prevent degradation of viral genome by the host restriction-modification antiviral defense system [1,3].

1: Computational identification of novel biochemical systems involved in oxidation, glycosylation and other complex modifications of bases in DNA. Iyer LM, Zhang D, Burroughs AM, Aravind L; Nucleic Acids Res. 2013;41:7635-7655. PMID:23814188

2: Pathways of thymidine hypermodification. Lee YJ, Dai N, Muller SI, Guan C, Parker MJ, Fraser ME, Walsh SE, Sridar J, Mulholland A, Nayak K, Sun Z, Lin YC, Comb DG, Marks K, Gonzalez R, Dowling DP, Bandarian V, Saleh L, Correa IR, Weigele PR; Nucleic Acids Res. 2022;50:3001-3017. PMID:34522950

3: Identification and biosynthesis of thymidine hypermodifications in the genomic DNA of widespread bacterial viruses. Lee YJ, Dai N, Walsh SE, Muller S, Fraser ME, Kauffman KM, Guan C, Correa IR Jr, Weigele PR; Proc Natl Acad Sci U S A. 2018;115:E3116. PMID:29555775