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Genetic separation of activating and repressing functions of the basic leucine zipper (bZIP) transcription factor Hac1ip on transcription

Final Activity Report Summary - HACREP (Genetic separation of activating and repressing functions of the basic leucine zipper (bZIP) transcription factor Hac1ip on transcription)

The aim of this work was to understand how one protein can activate directly opposing cellular functions and yet achieve a meaningful outcome for the cell that determines the cell's fate. The basic leucine zipper transcription factor Hac1ip both activates transcription and inhibits transcription. To activate transcription Hac1ip recruits a protein complex that acetylates chromatin proteins tightly associated with the DNA in eukaryotic cells to regulatory elements of certain genes. Acetylation of these chromatin proteins correlates in many cases with increased transcription or expression of the gene. To inhibit transcription Hac1ip activates a protein complex that catalyses the reversal of acetylation of the chromatin proteins. If regulation of both protein complexes by Hac1ip occurs on the same promoter, a net null outcome - except for wastage of cellular energy - should occur, because the acetylation put onto the chromatin proteins by the first complex is immediately removed by the second complex. Therefore, it is likely that the function of Hac1ip is regulated, in other words, in one environmental situation it can only activate the acetylating complex, and in another environmental situation Hac1ip activates the acetylation removing complex.

The objective of this work was to a) establish technology to perform a genetic screen to isolate Hac1ip mutants that can only activate or inhibit transcription, and b) to identify these mutants in an unbiased, uninformed genetic screen and in informed experimentation exploiting biochemical and genetic knowledge on the function of other transcription factors closely related to Hac1ip. These mutants, once isolated, will be very helpful to identify which signalling events regulate Hac1ip function.

For these screens in a genetic model organism, Baker's yeast, three components are required:
1) a drug-regulatable expression system for Hac1ip,
2) a reporter gene reporting on transcriptional activation by Hac1ip, and
3) a second, different reporter gene reporting on inhibition of transcription by Hac1ip.

Important milestones in this work that need to be met before the screens can be executed are:
1) Construction of these materials, and
2) verification of functionality of these materials.

The project has made significant progress towards achieving its objectives and milestones. We have completed construction of all materials and have preliminarily verified the functionality of some of these materials. Verification of the other materials is currently on-going. This work should be completed within the next 6-12 months, after which a postgraduate student will execute the genetic screens.