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Marek’s Disease Virus | 349
DNA Pol

UL
TRL IRL
UL2 UL5 UL8 UL9 UL12 UL23 UL29 UL30 UL39 UL40 UL42 UL50 UL52
RR

DNA H-P

Figure 12.1 DNA replication associated genes of the MDV. The unique long (UL) region is flanked by terminal (TRL) and internal repeat
long (IRL) regions. The location of the origins of replication is indicated by vertical arrows. The essential and non-essential DNA replication
associated genes are listed (black and grey, respectively). The subunits of DNA polymerase (DNA Pol), DNA helicase and primase (DNA H-P),
and ribonucleotide reductase (RR) are shown.
Figure 1

Table 12.4 MDV proteins involved in replication.
HSV Alternate Essential for DNA
MDV gene homologue Protein abbreviation synthesis Major function
MDV021 UL9 Origin-binding protein OBP Yes Origin-binding protein
3’–5′ DNA helicase
MDV042 UL29 Major single-stranded ICP8, SSB, Yes Single-stranded DNA-binding protein;
DNA-binding protein MDBP Single-strand annealing protein;
Stimulates DNA polymerase,
helicase-primase, and origin binding protein
MDV017 UL5 DNA helicase-primase Yes Subunit of helicase-primase;
Contains helicase motifs
MDV020 UL8 DNA helicase-primase Yes Subunit of helicase-primase;
Stimulates primer synthesis, interacts with
ICP8 and OBP proteins
MDV066 UL52 DNA helicase-primase Yes Subunit of helicase-primase;
Contains primase motifs
MDV043 UL30 DNA polymerase Pol Yes Catalytic subunit of DNA polymerase;
3’–5- exonuclease, RNase H
MDV055 UL42 DNA polymerase Yes Processivity subunit of DNA polymerase;
Double-strand DNA-binding protein
MDV024 UL12 Alkaline nuclease 5′–3′ Exo No Endo- and exonuclease;
Interact with ICP8;
Viral recombinase
MDV014 UL2 Uracil DNA glycosylase UDG No Uracil-DNA glycosylase
MDV063 UL50 Deoxyuridine triphosphatase dUTPase No Deoxyuridine triphosphatase
MDV036 UL23 Thymidine kinase TK No Non-specific nucleoside kinase
MDV052 UL39 Ribonucleotide reductase RR1, ICP6 No Large subunit of ribonucleotide reductase
MDV053 UL40 Ribonucleotide reductase RR2 No Small subunit of ribonucleotide reductase

Two-subunit DNA polymerase (MDV043/UL30 and Proteins associated with viral DNA replication
MDV055/UL42, Pol) Although these proteins are not required for DNA replication in
MDV DNA polymerase exists as a heterodimer, which includes cultured cells, they are involved in nucleotide metabolism and
the protein products of MDV043 or UL30 and MDV055 or UL42 have certain effect on the cell growth and viral spread.
genes. UL30, a 1180 amino acid long protein, possesses both 3′–5′
exonuclease and RNase H activities. On the other hand, UL42, a Alkaline nuclease (MDV024/UL12)
488 amino acid long phosphoprotein, possesses double-strand MDV alkaline nuclease is encoded by MDV024, a homologue of
DNA binding activity, and works as the DNA polymerase proces- HSV-1 UL12 (Osterrieder, 1999). It has endo- and exonuclease
sivity factor (Sui et al., 1995). activities and shows no sequence specificity (Banks et al., 1983).