Community effects in regulation of translation.

Genes encode the instructions needed to make proteins and other molecules. To make a protein, the DNA within a gene is copied to produce molecules of messenger ribonucleic acid (mRNA) that are then used as templates to build proteins via a process called translation. This process – which involves protein machines called ribosomes binding to the start of the mRNA – is tightly regulated to control the amounts of particular proteins in cells. For example, in fruit fly ovaries, a protein called Bruno both represses and activates the translation of a gene known as oskar. To achieve this, Bruno binds to regions near the end of the oskar RNA known as Bruno response elements. It is not clear how Bruno acts to control translation. However, because ribosomes begin translation near the start of the mRNA, while Bruno is bound to regions near the end of the mRNA, there must be long-range interactions between the two ends of the mRNA. It is generally assumed that such long-range interactions only occur between proteins that are bound to the same mRNA molecule. However, in 2010, researchers observed that Bruno response elements within one oskar mRNA could influence the translation of other oskar mRNAs. This is known as “regulation in trans”. Here, Macdonald et al. – including some of the researchers from the earlier work – investigated this observation in more detail in fruit flies. In cells, multiple mRNA molecules and their associated proteins can assemble into particles. Macdonald et al. proposed that the close proximity of many mRNA molecules in these particles could allow trans regulation to take place. Indeed, the experiments found that blocking the assembly of oskar mRNA into particles inhibited trans regulation as expected. Macdonald et al. also asked if trans regulation can occur between mRNAs that encode different proteins. The experiments show that oskar mRNA could block the translation of an mRNA produced by the gurken gene, even when oskar mRNA was not being translated. More work is needed to find out how widely trans regulation is used to control translation.