• Question from:Becca

Hello

I am trying to work out exactly what an ORFan gene is:

Here is my understanding of an ORFan gene, I have two different definitions that I have found but put in my own words to try and make sense of them:

1) An ORFan gene is a supposed Open Reading Frame that does not resemble any protein coding sequence previously identified in any other genome other than that particular genome where the ORFAn gene is (or in closely-related organisms).

2) An ORFan gene is a supposed Open Reading Frame that does not resemble any protein coding sequence previously identified but does code for a protein.

Is an ORFan gene actually a gene? Do they know the functions of ORFan genes?

How do ORFan genes differ from "junk" DNA?

I only have basic biological understanding so simplifications appreciated!

Many thanks

Becca

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  • University of Bristol
  • Posts: 2,463

The term means different things to different people which is why you are confused! I prefer "orphan" since ORFan only applies to bacteria.

An orphan gene is one that codes for a protein which has no known homologue in other species/genomes. In orther words point 1 above.

Some people however use "orphan" to denote a receptor where the ligand is not yet known.

Since both of the above refer to genes that code for proteins then they are not "junk" DNA. Indeed the term junk has largely been superceded - it is now clear that non-coding regions of DNA play vital functions such as regulating the sites, timing and levels of expression of almost all genes that code for proteins.

Hope that helps.

  • University of Bristol
  • Posts: 349

As the bacterial ORFan gene's function is known it will usually be registered in the databases under a new gene name. As David says we use the word "orphan" to denote a receptor where the ligand is not known, and it becomes 'de-orphanated' when the scientific community is satisfied that it's ligand has been established (e.g., a number of scientists have repeated the observation) - although we may now know the ligand for the orphan receptor we can still be a long way off establishing its function in the body.