Bioinformatics and Genomics News and Views » yeast

iRNA in yeast

Jessica P. — Fri, 27 Nov 2009 16:16:23 +0000

iRNA is a tool currently used in molecular biology to define the function of a gene: indeed scientists block mRNA transcription of specific gene and observe the cellular response. This technique is extremely potent and specific and allows to study one protein at time. In yeast, certain strains lack the normal RNA interference machinery and have alternative enzyme variants which can be transplanted into truly deficient species. iRNA is specially useful to study budding yeast, but this model lacks the Dicer enzyme, responsible for processing the double stranded RNAs into small interfering RNAs.
Scientists from the Whitehead Institute identified many proteins that show hallmarks of Dicer- mediated cleavage; they moved these proteins into new strains in order to reconstitute the iRNA machinery and they observed the complete silencing of all gene of interest. Thus, no limitations were found to study genes and proteins involved in yeast biology. Moreover, transposons are efficiently silenced without interfering with other genes. The system is greatly specific. Based on this positive result, scientists want to apply this finding to pathogenic yeast Candida Albicans in order to better understand the behaviour of this organism and identify some pharmacological target.

Manipulation of bacterial genome in yeast

Jessica P. — Wed, 28 Oct 2009 15:14:07 +0000

Even if manipulation of bacterial genome is often difficult and challenging, engineering allows to better understand bacterial biology and genetics. Researchers from C. Venter Institute improve a protocol to clone bacterial genome in yeast, manipulate it and boot it up in bacteria self. To do this they chose an “easy” model, Mycoplasma, because this organism doesn’t have bacterial wall, its genome is small and A-T rich, so is more properly replicated in yeast than ones rich in G-C. Furthermore Mycoplasma has non-standard genetic code that can not be translated in yeast, preventing the synthesis of bacterial proteins toxic for yeast.

What did scientists perform to achieve this important result? They cloned Mycoplasma genome into yeast artificial chromosomes (YACs), genetically manipulated it and then transplanted it into the final organism receiver. Two concerns could prevent this goal: one was the possibility that restriction endonucleases recognised foreign sequences and degraded them and the second one was that yeast modified bacterial genome. Fortunately this last event didn’t occur, while to limit endonucleasic activity, scientists hypermethylated donor genome and eliminated endonucleases from receiver organism. This protocol could be improved in order to become a conventional technique for bacterial manipulation in order to have another tool to solve human needs in medicine and environmental preservation.

Microinjection of yeast

Jessica P. — Thu, 20 Aug 2009 15:46:18 +0000

Yeast is a commonly used genetic model, budding and fission have been largely studied, but few methods to introduce DNA, protein or other compounds, have been described until now. Indeed, yeast presents the rigid cell wall that avoids injection and all techniques currently used to manipulate cells. It has been described that piezo-impact micromanipulator worked well to overcome biological barriers; thus, this tool was employed also for yeast injection with good results.

The procedure, reported in the last volume of Nature Methods, allows to introduce material during fission yeast. At the microscope it’s possible to immobilize and buckle one cell, through mechanical stress, while sorbitol in the surrounding medium avoids cell disruption. Material that has to be injected enter into the cell is released from pipette and passed through the hole into the wall. The major difference between usual microinjection technique is that the pipette doesn’t touch cell surface. Why is this method so innovative? For the first time yeast has been manipulated and now inhibitors, RNA and proteins could be introduced in. Thus, new experiments could be thought and performed, keeping in mind that yeast is really diffused, as a tool for genetic studies and recombinant protein expression and other applications could be now imaged.