DNA's protein-building instructions may be able to combine in an unexpected way, increasing the number of possible proteins that can be generated from a given number of genes, according to a report in this week's Nature.
The new finding may have important implications for scientists puzzled by last week's announcement that an initial survey of the human genetic code had found an unexpectedly small number of genes.
Traditional scientific thinking supposes that instructions for building a protein are encoded on one strand of the double-stranded DNA molecule. Researchers at The Johns Hopkins University's Kreiger School of Arts and Sciences identified a fruit fly protein whose instructions follow one strand of the DNA molecule, but also include a segment that follows the opposite strand, which "reads" in the opposite direction.
"We've known for some time that one gene can make multiple protein products," says Victor Corces, chairman of biology and an author of the paper. "The process we're reporting on, which is called trans-splicing, increases even further the possibility of making additional protein products from just two genes."
Trans-splicing had been seen before in a few genes in plant cells and microorganisms, but had never before been shown to be essential to the function of an important protein.
Corces and his co-authors found the trans-splicing while studying the fruit fly gene known as mod (mdg4). They had identified two mutations that could disrupt the function of the gene, and showed that putting either of those mutations in both of the fruit fly's two copies of mod(mdg4) disabled a critical protein made by the gene.
However, when they placed one type of fatal mutation in one copy of the gene and a different kind of fatal mutation in the other copy, the critical protein continued to be made.