- This web page was produced as an assignment for an undergraduate course at Davidson College -

My Favorite Yeast Expression: EST1

EST1 is known to associate with telomerase and assist in telomere maintenance.  Using Expression Connection and the scale provided below, I have isolated the public-domain experiments where EST1 undergoes a repression or induction change of at least |2|. 

Perhaps the most significant experiment involving an induction of EST1 is in response to DNA damaging agents (Gasch et al., 2001).  This experiment found a +3.1 increase in EST1 fold induction in response to gamma irradiation at a certain time point.  Interestingly, this expression only appeared for a very brief time, and only appeared in wild-type irradiated cells.  No other genes were found with similar expression profiles (with Pearson correlation of >0.8).  The microarray data from that experiment are pictured below.

Another interesting experiment involving an induction of EST1 is in response to histone depletion (Wyrick et al., 1999).  Histones are proteins used by the cell to package DNA in increments called nucleosomes.  The authors found that histones make contributions to telomeric silencing, so when histones were depleted, telomeric genes were generally induced.  The induction pattern for EST1 over time (as well as 20 other similarly expressed genes with Pearson correlation of >0.8) is shown below.  Additionally, a graph depicting expression of EST1 (YLR233C) in response to histone depletion is also shown below.

Finally, the last experiment with >2 induction of EST1 is in response to environmental changes (Gasch et al., 2000).  This experiment explored environmental conditions including chemical treatments of ethanol, glucose, and diamide as well as various degrees of heat shock.  Most results for EST1 were not particularly interesting, except Nitrogen depletion over several days.  No correlated genes were found, but remember that the program tries to correlate all data points, which includes all experimental conditions.  I have truncated the data display and reprinted the segment involving nitrogen depletion below.

Only one experiment of note indicated a significant degree of fold repression.  In response to alpha factor (Roberts et al., 2000) -  a yeast pheromone - EST1 was silenced over time.  A list of the genes with a >0.8 Pearson correlation below also includes TEL2, a telomeric DNA binding protein, as having a similar expression profile in response to alpha factor.  The graph below also describes the very high magnitude of fold repression of EST1 during this experiment.

Finally, another database may be consulted to describe the expression of EST1.  Function Junction is an online tool capable of searching many database resources, including the Yeast Microarray Global Viewer (from the Laboratoire de Genetique Moleculaire in Paris, France).  Results from this search are pictured below.  Each box represents a unique experiment involving yeast genes and various experimental conditions.  One experiment of note is Jelinski Rpn4 whereby cells were damaged and EST1 displays a strong fold induction profile.

These online database searches serve to confirm the known role of EST1 in telomere maintenance.  During stressful conditions including histone depletion, DNA damage, and nitrogen depletion, EST1 is induced.  In response to a mating factor, however, the gene is repressed.  This indicates that EST1 is designed to protect the cell from conditions potentially damaging to telomeres, but must be turned off in situations where DNA is required (such as mating).  In future searches, proteomic databases will be consulted to better characterize EST1.

For more data from this assignment, go to My Favorite Yeast Expression of YLR243W.

This page created by: Gray Lyons

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