Breakthrough

Scientists have created the first synthetic chromosome for yeast in a landmark for biological engineering.

Previously synthetic DNA has been designed and made for simpler organisms such as bacteria.

As a form of life whose cells contain a nucleus, yeast is related to plants and animals and shares 2,000 genes with us.

So the creation of the first of yeast's 16 chromosomes has been hailed as "a massive deal" in the emerging science of synthetic biology.

The genes in the original chromosome were replaced with synthetic versions and the finished man made chromosome was then successfully integrated into a yeast cell.

The new cell was then observed to reproduce, passing a key test of viability.

Yeast is a favoured target for this research because of its well-established use in key industries such as brewing and baking and its potential for future industrial applications.

One company in California has already used synthetic biology to create a strain of yeast that can produce artemisinin, an ingredient for an anti-malarial drug.

The synthesis of chromosome III in yeast was undertaken by an international team and the findings are published in the journal Science (yeast chromosomes are normally designated by Roman numerals).

Dr Jef Boeke of the Langone Medical Centre at New York University, who led the team, described the achievement as "moving the needle in synthetic biology from theory to reality".

In an interview with BBC News, he said: "What's really exciting about it is the extent to which we have changed the sequence and still come out with a happy healthy yeast at the end."

The new chromosome, known as SynIII, involved designing and creating 273,871 base pairs of DNA - fewer than the 316,667 pairs in the original chromosome.

The researchers removed repeated sections in the original DNA and so-called "junk" DNA known not to code for any proteins - and they then added "tags" to the chromosome.

Dr Boeke said that despite making more than 50,000 changes to the DNA code in the chromosome, the yeast was not only "hardy" but had also gained new functions.

"We have taught it a few tricks by inserting some special widgets into its chromosome."

One new function is a chemical switch that allows researcher to "scramble" the chromosome into thousands of different variants making genetic manipulations far easier.  Read more.