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Genes are not linear sequences of DNA that directly correspond one-to-one with their protein counterparts. Moreover, scientists now know that not all transcribed RNA molecules, or transcripts,...
-In living cells, RNA is usually a double-stranded molecule, while DNA can often be single-stranded. In viruses called retroviruses, the genetic information is contained in RNA; these viruses have no DNA. These viruses also have an enzyme called reverse transcriptase. What is its function?
These viruses combine a gene for a polyomavirus-like replication protein with genes for structural and morphogenetic proteins homologous to those encoded by adenoviruses. This is another, remarkable case of virus chimerism.
HPVs are double-stranded DNA viruses with a genome of approximately 8.000 base pairs encoding eight “early” (E) and “late” (L) viral proteins. You might find these chapters and articles relevant to this topic. R. Hull, in Encyclopedia of Applied Plant Sciences, 2003.
For example, circoviruses get by with only two genes: one to encode the capsid protein that will protect and deliver the genome in the infectious virus, and a replicase protein that hijacks cellular polymerases to create new copies of the viral single-stranded DNA genome.
Both of these examples show a high density of coding information. In influenza virus, genes 7 and 8 both encode two proteins in overlapping reading frames. In geminiviruses, both strands of the virus DNA found in infected cells contain coding information, some of which is present in overlapping reading frames.
In summary, there are four genes in this region, and they are the sets of sequences shown inside the orange dashed lines: Gene 1 consists of the sequence segments A, B, and C; gene 2 consists of D; gene 3 of E; and gene 4 of X and Y.
