Conjoined gene
Encyclopedia
A conjoined gene is defined as a gene
, which gives rise to transcripts by combining at least part of one exon from each of two or more distinct known (parent) genes which lie on the same chromosome, are in the same orientation, and often (95%) translate independently into different proteins. In some cases, the transcripts formed by CGs are translated to form chimeric or completely novel proteins.
Figure 1: Cartoonic representation of the formation of conjoined gene A-B from parent genes A and B.
Several alternative names are used to address conjoined genes, including combined gene and complex gene (both from Roginski et al, "The human GRINL1A gene defines a complex transcription unit, an unusual form of gene organization in eukaryotes" Genomics 84: 265-276, 2004. pmid=15233991), fusion gene
, fusion protein
, read-through transcript, co-transcribed genes, bridged genes, spanning genes, hybrid genes, locus-spanning transcripts, etc.
At present, 800 CGs have been identified in the entire human genome by different research groups across the world including Prakash et al., Akiva et al., Parra et al., Kim et al., and in the 1% of the human genome in the ENCODE pilot project. 36% of all these CGs could be validated experimentally using RT-PCR and sequencing techniques. However, only a very limited number of these CGs are found in the public human genome resources such as the Entrez Gene database
, the UCSC Genome Browser
and the Vertebrate Genome Annotation (Vega) database
. More than 70% of the human conjoined genes are found to be conserved across other vertebrate genomes with higher order vertebrates showing more conservation, including the closest human ancestor, chimpanzee. Formation of CGs is not only limited to the human genome but some CGs have also been identified in other eukaryotic genomes, including mouse and drosophila. There are a few web resources which include information about some CGs in addition to the other fusion genes, for example, ChimerDB
and HYBRIDdb. Another database, ConjoinG, is a comprehensive resource dedicated only to the 800 Conjoined Genes identified in the entire human genome.
Gene
A gene is a molecular unit of heredity of a living organism. It is a name given to some stretches of DNA and RNA that code for a type of protein or for an RNA chain that has a function in the organism. Living beings depend on genes, as they specify all proteins and functional RNA chains...
, which gives rise to transcripts by combining at least part of one exon from each of two or more distinct known (parent) genes which lie on the same chromosome, are in the same orientation, and often (95%) translate independently into different proteins. In some cases, the transcripts formed by CGs are translated to form chimeric or completely novel proteins.
Several alternative names are used to address conjoined genes, including combined gene and complex gene (both from Roginski et al, "The human GRINL1A gene defines a complex transcription unit, an unusual form of gene organization in eukaryotes" Genomics 84: 265-276, 2004. pmid=15233991), fusion gene
Fusion gene
A fusion gene is a hybrid gene formed from two previously separate genes. It can occur as the result of a translocation, interstitial deletion, or chromosomal inversion...
, fusion protein
Fusion protein
Fusion proteins or chimeric proteins are proteins created through the joining of two or more genes which originally coded for separate proteins. Translation of this fusion gene results in a single polypeptide with functional properties derived from each of the original proteins...
, read-through transcript, co-transcribed genes, bridged genes, spanning genes, hybrid genes, locus-spanning transcripts, etc.
At present, 800 CGs have been identified in the entire human genome by different research groups across the world including Prakash et al., Akiva et al., Parra et al., Kim et al., and in the 1% of the human genome in the ENCODE pilot project. 36% of all these CGs could be validated experimentally using RT-PCR and sequencing techniques. However, only a very limited number of these CGs are found in the public human genome resources such as the Entrez Gene database
Entrez
The Entrez Global Query Cross-Database Search System is a powerful federated search engine, or web portal that allows users to search many discrete health sciences databases at the National Center for Biotechnology Information website...
, the UCSC Genome Browser
UCSC Genome Browser
The University of California, Santa Cruz is an up-to-date source for genome sequence data from a variety of vertebrate and invertebrate species and major model organisms, integrated with a large collection of aligned annotations...
and the Vertebrate Genome Annotation (Vega) database
Vertebrate and Genome Annotation Project
The Vertebrate and Genome Annotation project provides manual curation of vertebrate genomes for the scientific community. The Vega data repository is publicly available, regularly updated and includes annotations of several finished vertebrate genome sequences: human, mouse, zebrafish, pig and...
. More than 70% of the human conjoined genes are found to be conserved across other vertebrate genomes with higher order vertebrates showing more conservation, including the closest human ancestor, chimpanzee. Formation of CGs is not only limited to the human genome but some CGs have also been identified in other eukaryotic genomes, including mouse and drosophila. There are a few web resources which include information about some CGs in addition to the other fusion genes, for example, ChimerDB
ChimerDB
ChimerDB is a database of fusion sequences...
and HYBRIDdb. Another database, ConjoinG, is a comprehensive resource dedicated only to the 800 Conjoined Genes identified in the entire human genome.