A nested gene is a

gene In biology, the word gene (from , ; "... Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' or ''birth'' or ''gender'') can have several different meanings. The Mendelian gene is a b ...

whose entire coding sequence lies within the bounds (between the start codon and the

stop codon In molecular biology (specifically protein biosynthesis), a stop codon (or termination codon) is a codon ( nucleotide triplet within messenger RNA) that signals the termination of the translation process of the current protein. Most codons in ...

) of a larger external gene. The

coding sequence The coding region of a gene, also known as the coding sequence (CDS), is the portion of a gene's DNA or RNA that codes for protein. Studying the length, composition, regulation, splicing, structures, and functions of coding regions compared to no ...

for a nested gene differs greatly from the coding sequence for its external host gene. Typically, nested genes and their host genes encode functionally unrelated proteins, and have different expression patterns in an organism. There are two categories of nested genes: * genes nested within an

intron An intron is any nucleotide sequence within a gene that is not expressed or operative in the final RNA product. The word ''intron'' is derived from the term ''intragenic region'', i.e. a region inside a gene."The notion of the cistron .e., gene ...

of a larger gene * genes which lie opposite the coding sequence of a larger gene

Nested intronic genes

A nested intronic gene lies within the non-coding intronic region of a larger gene, and occurs relatively frequently, especially in the introns of

metazoans Animals are multicellular, eukaryotic organisms in the biological kingdom Animalia. With few exceptions, animals consume organic material, breathe oxygen, are able to move, can reproduce sexually, and go through an ontogenetic stage in ...

and higher

eukaryotes Eukaryotes () are organisms whose cells have a nucleus. All animals, plants, fungi, and many unicellular organisms, are Eukaryotes. They belong to the group of organisms Eukaryota or Eukarya, which is one of the three domains of life. Bact ...

. Because only eukaryotic DNA contains intronic regions, this type of gene does not occur in

bacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were am ...

or archaea.. The

human genome The human genome is a complete set of nucleic acid sequences for humans, encoded as DNA within the 23 chromosome pairs in cell nuclei and in a small DNA molecule found within individual mitochondria. These are usually treated separately as the ...

contains a relatively high proportion of nested intronic genes. It is predicted to contain at least 158 functional intronic nested genes, with an additional 212

pseudogenes Pseudogenes are nonfunctional segments of DNA that resemble functional genes. Most arise as superfluous copies of functional genes, either directly by DNA duplication or indirectly by reverse transcription of an mRNA transcript. Pseudogenes are ...

and three

snoRNA In molecular biology, Small nucleolar RNAs (snoRNAs) are a class of small RNA molecules that primarily guide chemical modifications of other RNAs, mainly ribosomal RNAs, transfer RNAs and small nuclear RNAs. There are two main classes of snoRNA, ...

genes nested in intronic regions. These genes seem to be distributed randomly across all

chromosomes A chromosome is a long DNA molecule with part or all of the genetic material of an organism. In most chromosomes the very long thin DNA fibers are coated with packaging proteins; in eukaryotic cells the most important of these proteins are ...

, and the majority code for proteins that are functionally unrelated to their host genes.

Genes nested opposite coding sequences

Genes nested opposite the coding sequences of their host genes are very rare, and have been observed in

prokaryotes A prokaryote () is a single-celled organism that lacks a nucleus and other membrane-bound organelles. The word ''prokaryote'' comes from the Greek πρό (, 'before') and κάρυον (, 'nut' or 'kernel').Campbell, N. "Biology:Concepts & Conn ...

, and more recently, in yeast ( ''S. cerevisiae'') and in ''Tetrahymena thermophila''. These non-intronic nested genes remain to be identified in

metazoan Animals are multicellular, eukaryotic organisms in the biological kingdom Animalia. With few exceptions, animals consume organic material, breathe oxygen, are able to move, can reproduce sexually, and go through an ontogenetic stage in ...

genomes. As with intronic nested genes, nonintronic nested genes typically do not share functions or expression patterns with their host genes.

References

External links

{{Genetic recombination Molecular biology Molecular genetics

Nested intronic genes

Genes nested opposite coding sequences

See also

References

External links