YMGV provides a graphical view of gene ratio distribution along the yeast chromosomes for each experiment. This feature is directly accessible by selecting the "expression map for one experiment" on the yMGV homepage. With this tool, you can easily visualize the chromosome localisation of co-expressed genes clusters.

If we perform such a global search on the 1030 conditions available in yMGV, such gene expression domains are clearly observable.On this figure is represented the three main experiments where such regulations are observed; i.e. in the publication on TUP1 transcription factor (A., DeRisi et al., 1997; and B., Hughes et al., 2000) and on deacetylation (C, Bernstein et al., 2000). The expression map represents the base 2 logarithm of the ratio for each gene along the entire chromosome. The chromosomes XI to XVI are represented. The induced (red) or repressed (green) telomeric region are clearly observable. In the DeRisi’s experiment (A), the chromosome XIII global repression is also visible and is probably due to an aneuploïdy phenomenon.

With a closer look, we see that in the DeRisi et al. experiment on TUP1 deletion (DeRisi et al., 1997) , all the telomeric regions seem to be subject to up regulation.

This is in relation with the role of TUP1 in transcriptional repression at the telomeres. In addition, the chromosome XIII seems globally down-regulated. Interestingly, a similar TUP1 deletion was studied by another team (Hughes et al., 2000), where similar effects on telomeric regions is observed using yMGV, but no specific regulation was seen on the chromosome XIII.

The down regulation observed in the DeRisi's experiments could be related to an aneuploidy phenomenon ([Hughes et al., 2000). Similarly, a global down-regulation of 40% of endogenous genes located within 20kb of telomeres is shown in RPD3 deletion experiment (Bernstein et al., 2000).

Rpd3p is involved in gene activation and silencing in yeast. This result has to be related with Tup1p association with histone deacetylation which has been shown previously (Bone et al., 2001; Wu et al., 200). In addition, in the experiment with Gal4 chromatin immunoprecipitation on glucose media (Ren et al., 2000) a similar telomeric regulation is observed but with a less extend.

It has been described before that Tup1p is involved in glucose repression in Saccharomyces cerevisiae (Williams et al., 1991) in association with other DNA-binding repressor by acting as a multi-protein complex (PArk et al. 1999). So Gal4p DNA binding target and Tup1p region of DNA association could be co-localized in telomeric regions.

These few examples enhance the importance of yMGV chromosome display which can actually reveal fundamental unexpected features of gene expression.