Researchers have determined the function of a new family of proteins associated with cancer and autism. Cells constantly make new proteins under the guidance of the genetic programme. Proteins are chains of amino acids synthesized by a special molecular machine, the ribosome.

Amino Acid Sequence

The amino acid sequence is encoded in a template, the mRNA molecule, and the decoding and synthesis process is called translation. In order to synthesize the right protein, a ribosome must attach to mRNA, find the correct point for starting the synthesis, then read the entire coding region and release the finished protein.

All these translation stages are already relatively well understood, but the fate of the ribosome after it has finished its work remained elusive. The study was published in Molecular Cell.

In the new study, researchers studied a family of proteins that includes MCT-1, a product of an oncogene, its partner DENR, which is associated with autism, and the translation factor elF2D.

Biochemical Activity

They discovered factor elF2D as early as 2010. They characterized its biochemical activity but, at that time, there was no clear evidence of the role played by this protein in the living cell.  Since then, a number of high-impact papers have been published suggesting that eIF2D and two similar factors, MCT-1 and DENR, can be involved in reading a special class of mRNA.

These mRNA molecules have additional short reading frames, so-called uORFs, before the main coding region that encodes the main protein. A ribosome can also read such uORFs. In many cases, this prevents the ribosome from reaching the main coding region, thereby regulating the production of the main protein.

Human mRNAs

As short uORFs are present in approximately half of the human mRNAs, it was important to find the possible role of eIF2D, MCT-1, and DENR in their translation. Attempts to pinpoint the function of their factors or shed light on how they work in the human body remained unsuccessful.

Thus, they turned to simpler organisms, such as yeast, they worked with yeast strains that had no genes of these factors. Our partners from the National Institutes of Health, U.S., applied ribosome profiling, allowing translation in mutant cells to be studied systematically, while we took on the biochemical part.

Translating Ribosomes

Ribosome profiling is based on high-throughput sequencing of millions of small mRNA fragments covered by translating ribosomes. This breakthrough technique shows the full picture of protein biosynthesis in a cell at a particular moment.

In our laboratory, this method is used to study translation in mammalian cells. But our American colleagues applied it to yeast. However, the data obtained with such systems approaches should be verified by classical methods to avoid misleading interpretations.

To this end, they used cell-free translation systems. They prepared yeast cell extracts, added mRNA that had been synthesized in a test tube and observed how much product was synthesized from these RNA molecules in the case of yeast strains with or without mutations in a particular gene.

Neuronal Development

This collaboration allowed the researchers to find out that factors eIF2D, MCT-1 and DENR are required for the ribosome to detach timely from the mRNA once the translation is complete. Apparently, the oncogenic potential of MCT-1 and disruptions of neuronal development associated with mutations in the DENR gene are linked to the role of these factors in the translation of uORF-containing mRNA, many of which encode important regulators of cellular processes.