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Minimum Genome: How Many Genes Do You Really Need? 473 Will Do For a Start

2016-03-24

Humans have about 22,000 separate genes; each gene codes for a protein that functions as part of the body, whether as an enzyme, a hormone, or a part of the body’s structure.  Single-celled organisms have fewer genes, and there are some organisms that have many more genes.  No-one knows for sure how many of these genes are really needed, and it is possible that some could be removed without impairing our function.

How many genes are essential for survival as a single free-living organism?  Less than 500.  Scientists have built a free-living bacterium related to the Mycoplasma family that has only 473 genes.  This report in Science News describes the research that led to the production of this synthetic Mycoplasma.  The Mycoplasma mycoides  bacterium that the scientists used as the starting point for this experiment had 901 genes.  Of the 473 essential genes, they were unable to determine the exact function of 149; of these, some 79 are completely mysterious.

At first, the research tried to create a genome with only known genetic parts, but it didn’t work.  Once they added the genes with uncertain functions, the cell began to work properly.  Of the genes with known functions, there were four broad classes: those that kept the cell membrane intact, those that expressed information from the genome, those that ran the metabolism (breaking down “food” and obtaining energy ), and finally those that helped preserve the genome in one piece.

While this accomplishment is less than perfect (over 17% of the basic genes have unknown functions) it is nonetheless dramatic.  The people responsible are the J. Craig Venter Institute in La Jolla, CA; this nonprofit foundation was started by Venter for the express purpose of studying genomes.  According to their web site, the Institute was formed in 2006 from the merger of  five separate research organizations.  It has 250 scientists at two sites: Rockville, MD, and La Jolla CA.  Dr. Venter was at the National Institutes of Health (NIH) in 1991 when he started deciphering genes and discovered new tools for rapidly analyzing genomes.  He started a group called The Institute for Genomic Research, a nonprofit dedicated to reading genomes.  In 1995, the NIH team read the genome of Hemophilus influenzae, the first free-living organism to have its genome sequenced.  The human genome was sequenced in 2001.

Now the group (and others) can focus on discovering the functions of the unknown genes, and more importantly, on discovering how multicellular organisms structure themselves through their genomes.  The last fifty or sixty years have seen amazing advances in genetic research, from the discovery of the structure of DNA by Watson and Crick to the sequencing of the human genome by Celera Genomics and the National Institutes of Health through the Human Genome Project.  In the last fifteen years since the human genome was sequenced, research has continued apace, and the minimal synthetic organism is the latest product.

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