Gene Expression

The Mimivirus genome exhibits similar transcription encoding genes found in Poxviridae. These similarities suggest that the transcription of Mimivirus occurs in the cytoplasm (Raoult, 2004). Mimivirus can encode a large number of genes (Legendre, 2011). These genes are placed in categories that are based on their function: translation, DNA repair enzymes, and chaperones (protein that assists folding and assembly). Where these genes play the role in Mimivirus is another story. Mimivirus possesses 6 tRNAs known to be three Leu, one Trp, one Cys, and one His. Functions of some gene expression in Mimivirus are still unknown, further investigations are preceded. Table 1 shows a list of genes found in the Mimivirus and its possible functions.

In addition to these tRNAs, the Mimivirus also exhibits proteins that are in charge of translation. These are known to be aminoacyl-tRNA synthetases, translation initiation factor 4E (e.g. mRNA cap binding) and much more (Raoult, 2004). Sources did not provide information on how or when Mimivirus use these proteins. Based on what was found, there are two large RNA polymerase II subunits which are known to be genes R501 and L244. The Mimivirus also have four smaller RNA polymerase II subunits: R470, L235, R209, and L376. The function of RNA polymerase II is to synthesize mRNA from DNA. Again, it was not known when Mimivirus use RNA polymerase II. Mimivirus also possesses a poly (A) tail, which is known to be gene R341, and a series of transcription factors such as L250, R339, R350, R429, R450, and R559.

Mimiviruses contains a few DNA topoisomerases. These DNA topoisomerases are enzymes that function in fixing problems involving DNA replication, transcription, and recombination (process by which nucleic acids break and join another nucleic acid). R480, R194, and L221 are some examples of DNA topoisomerases found in the Mimivirus.

Genomes can be damaged by chemicals, ultraviolet light, or radiations (Raoult, 2004). The Mimivirus possesses several DNA repair enzyme, which for its purpose, prevent DNA errors. These include L315 and L720 genes, which locates oxidized purines and cuts it off. Mimivirus genome possesses an UV-damage endonculease. This enzyme serves to take away any UV damaged DNA off. L386 and R555 are genes in charge of repair for UV damaged DNA. Another DNA repair enzyme is L359, which is involved in DNA mismatch repair. Overall, Mimivirus seemed well equipped with repair mechanisms (Raoult, 2004). Due to this ability, Mimivirus particles have capabilities in being resistant to harsh conditions. However, if 35 kilograys of gamma rays or UV light were exposed to the genome for 15 minutes, then that would instantly kill the Mimivirus, despite their ability in DNA repair (Raoult, 2004).


Table 1. Majorly identified Mimivirus genome. (Raoult, 2004). There are 1018 protein coding genes (including the new genes discovered) and 6 tRNAs in the Mimivirus. This table shows a list of genes found in the Mimivirus with its possible role and functions. dTDP = 3′-deoxy-thymidine-5′ diphosphate; ADP = adenosine 5′-diphosphate.


Mimivirus Newly Discovered Genes (Legendre, 2011) There are 1018 protein coding genes (including the new genes discovered) and 6 tRNAs in the Mimivirus. This reveals some of the recent new 75 genes found in 2011, list of genes generated from the fusion of previously identified ORFs, and list of deleted or renamed genes.


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