has within it a nucleus that contains, among other things, the information (DNA) to enable it to function properly. This information in turn, is divided into small segments, in packages that are called genes. Each gene, after being transcribed and translated, produces a special protein, ie each gene has enough information to synthesize a protein.
As experimental model, cells will be used yeast Saccharomyces cerevisiae is a unicellular eukaryotic organism non-pathogenic, easy handling, rapid growth in defined culture media and whose complete genome sequence is known. Taking into account the evolutionary conservation of the signaling pathways triggered in response to nutrient medium, the use of S. cerevisiae as a model for the study of signal transduction will clarify the major challenge is to understand how signals produced by nutrients present in the extracellular environment are integrated and coordinated by the cells. 
In this picture you can see a yeast cell gemando (reproducing asexually). can also observe the nucleus and vacuole.
UGA4 is the gene that codes for Uga4 protein. This protein is a permease located in the plasma membrane and allows the incorporation of d-aminolevúlico acid (ALA) 3.4 and y-aminobutyric acid (GABA) 5.6.
GABA can be used by the yeast cells as a source of nitrogen, but is a poor source in compared to rich sources of nitrogen and ammonia. Factors influencing the suppression or induction of gene expression, depending on the situation in which the cell is located. The gene to be expressed only in the absence of a source of nitrogen (as ammonium) in the absence of such a source, the cell triggers mechanisms to survive in such conditions. In the promoter sequence of the gene UGA4 two important sites known as GABA and UAS-UAS-GATA. In each of these factors influence the sticking repress or induce its expression. UGA4 gene expression depends on the presence of an inducer, GABA5, 7. Induction requires the action of two factors transcription, a specific Uga3 and other pleiotropic, Uga35, which act through activating sequence rich in GC nucleotides (UASGABA) 8.9. The UGA4 gene regulatory region also contains four adjacent repeats heptanucleótido 5'-CGAT (A / T) AG-3 'which is an UASGATA. On the latter acting GATA factors can act as positive and negative factors. The negative (and Gzf3 Uga43) compete with the positive (Gln3 and GAT1) and that "wins" sticks to the gene promoter. When there is a rich source of nitrogen, the cell does not waste energy synthesizing proteins carrying GABA8, 10.11, positive factors. Gln3 and GAT1, was found in the cytoplasm bound to the protein Ure2 from acting on the UAS-GATA element, and therefore, the negative factors "win", which leads to repression of the expression of UGA4. In this case the negative factors bind to the UAS-GATA site.
When there is a rich source but there are GABA in the medium, the cell adapts to change and active all the machinery to synthesize the protein Uga4, in other words, GABA induces gene expression UGA45, 7.9 . Positive factors dissociate from Ure2 and translocate to the nucleus where they move to the negative factors binding to the promoter and allowing expression gen9, 12. The interaction between the positive factors with GAT1 Gln3 and Ure2 is modulated by the phosphorylation status of these factors which in turn depends on the kinase activity Tor13-15.
The main objective of this internship is to familiarize with different molecular biology techniques through participation in a project that studies the signaling cascade that leads to the regulation of gene expression UGA4 by extracellular amino acids. Molecular mechanisms signaling cascade that is not fully understood but it is known that the SPS sensor complex is involved.
This complex is known as SPS16-18 for its three protein components (Ssy1p, Ptr3p and Ssy5p) and activated after the sensing of extracellular amino acids and possibly intracelulares19. Ssy1 is a membrane protein that resembles an amino acid permease but functions only as a sensor. Ssy5 ptr3 and interact with Ssy1 form a dynamic protein complex. It has been determined a large number of genes regulated by the activity of this sensor and many of these genes encode proteins involved in amino acid transport. Among them, AGP1 BAP2 and respond to amino acids via the SPS through Stp1 transcription factors, and Uga3520 STP2.
Stp1 and STP2 factors act in response to extracellular amino acid sensing on UASA elements present in promoters of permeases, such as BAP2 and BAP3. Importantly, the large sequence similarity between elements and UASGABA21 UASA, 22. STP2 Stp1 and are synthesized as latent factors and remain trapped in the cytoplasm through the amino terminal regulatory domain. Also three proteins in the inner nuclear membrane, ASI1, Asi3 ASI2 and participate in retaining and STP2 Stp1 latent in citoplasma23, 24. In response to amino acids, active Ssy1 Ssy5 protease that in turn cleaves the regulatory domain and STP2 Stp1, leading to activation of these factors. Their processed forms are transported to the nucleus where genes regulated transactivator SPS20 ,25-27.
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