The nucleocytoplasmic large DNA viruses or NCLDV refers to a number of families of large eukaryotic DNA virus

DNA virus

A DNA virus is a virus that has DNA as its genetic material and replicates using a DNA-dependent DNA polymerase. The nucleic acid is usually double-stranded DNA but may also be single-stranded DNA . DNA viruses belong to either Group I or Group II of the Baltimore classification system for viruses...

es:

1. Asfarviridae
   Asfarviridae
   Asfarviridae is a family of viruses that primarily infects swine, resulting in an onset of African swine fever. There is a single genus in this family: Asfivirus. The name of this family and genus are derived from the acronym: African swine fever and related viruses...
   
   
2. Iridoviridae
   Iridoviridae
   Iridoviridae are a family of viruses with double stranded DNA genomes. The name is derived from Iris the Greek goddess of the rainbow. This name was chosen because of the "rainbow like" iridescence observed in heavily infected insects and pelleted samples of invertebrate iridoviruses.-Taxonomy:The...
   
   
3. Marseilleviridae
   Marseilleviridae
   Marseilleviridae is a family of double stranded DNA viruses. It is a member of the nucleocytoplasmic large DNA viruses clade.-Taxonomy:There is one genus in this family and one species within this genus currently recognised. It was originally grouped with the Mimivirus but subsequent studies...
   
   
4. Megaviridae
5. Mimiviridae
   Mimiviridae
   Mimiviridae is a family of double stranded DNA viruses. Viruses in this family belong to the nucleocytoplasmic large DNA virus clade , a group which includes members of families Asfarviridae, Iridoviridae, Phycodnaviridae and Poxviridae and the genus Dinodnavirus.-Taxonomy:Although only a few...
   
   
6. Phycodnaviridae
   Phycodnaviridae
   Phycodnaviruses are large , double stranded DNA viruses that infect marine or freshwater eukaryotic algae...
   
   
7. Poxviridae
   Poxviridae
   Poxviruses are viruses that can, as a family, infect both vertebrate and invertebrate animals.Four genera of poxviruses may infect humans: orthopox, parapox, yatapox, molluscipox....
   
   

One unassigned genus Dinodnavirus

Dinodnavirus

Dinodnavirus is a genus of viruses that infect dinoflagellates. This genus belongs to the clade of nucleocytoplasmic large DNA viruses. The name is derived from 'di' and DNA ....

also belongs to this clade.

Reasons for NCLDV Grouping

All have both common and unique features of genomic DNA and virion structure. It remains uncertain whether the similarities of different families of this grouping of NCLDV are due to independent recruitment of the same or related host genes during viral replication or if they simply share a common viral ancestor, although the latter is under heavy scrutiny and controversy

There are 47 NCLDVs core genes currently recognised. These include the four key proteins are involved in DNA replication and repair. These include the enzymes DNA polymerase

DNA polymerase

A DNA polymerase is an enzyme that helps catalyze in the polymerization of deoxyribonucleotides into a DNA strand. DNA polymerases are best known for their feedback role in DNA replication, in which the polymerase "reads" an intact DNA strand as a template and uses it to synthesize the new strand....

 family B, the topoisomerase

Topoisomerase

Topoisomerases are enzymes that regulate the overwinding or underwinding of DNA. The winding problem of DNA arises due to the intertwined nature of its double helical structure. For example, during DNA replication, DNA becomes overwound ahead of a replication fork...

 II A, the Flap endonuclease

Endonuclease

Endonucleases are enzymes that cleave the phosphodiester bond within a polynucleotide chain, in contrast to exonucleases, which cleave phosphodiester bonds at the end of a polynucleotide chain. Typically, a restriction site will be a palindromic sequence four to six nucleotides long. Most...

 and the processing factor Proliferating Cell Nuclear Antigen. Other proteins include the DNA dependant RNA polymerase

RNA polymerase

RNA polymerase is an enzyme that produces RNA. In cells, RNAP is needed for constructing RNA chains from DNA genes as templates, a process called transcription. RNA polymerase enzymes are essential to life and are found in all organisms and many viruses...

 II and transcription factor

Transcription factor

In molecular biology and genetics, a transcription factor is a protein that binds to specific DNA sequences, thereby controlling the flow of genetic information from DNA to mRNA...

II B.

It is probable that these viruses evolved before the separation of eukaryoyes into the extant crown groups. The ancestral genome was complex with at least 41 genes including (1) the replication machinery (2) up to four RNA polymerase subunits (3) at least three transcription factors (4) capping and polyadenylation enzymes (5) the DNA packaging apparatus (6) and structural components of an icosahedral capsid and the viral membrane.