Saccharomyces cerevisiae as a tool to study human adenovirus E1A functions

Viral oncogenes have proven to be invaluable tools for probing the regulation of cellular processes. The E1A proteins are the immediate early gene products produced during an adenovirus infection. E1A functions include activating transcription of the other viral genes and promoting entry of the infected cell into S-phase. E1A is an oncogene which can fully transform cells in co-operation with a second oncogene, such as E1B. Numerous cellular proteins targeted by E1A have already been identified. The effects of E1A on the functions of many of these target proteins have not been determined.;Saccharomyces cerevisiae has been used extensively to understand the control of cellular processes. Certain strains of this yeast undergo pseudohyphal differentiation (PD) when starved for nutrients. The changes in growth and morphology that accompany PD are easily visualized and the highly conserved pathways that regulate PD are well characterized. I have identified two regions in E1A that modulate PD. (I) The first is a six amino-acid sequence in E1A, spanning residues 118-123 in conserved region 2. This portion of E1A targets yeast Ubc9p and its mammalian equivalent UBC9 (a SUMO conjugase). Mutational analysis revealed that E1A binds UBC9 very similarly to SUMO. Based on this information, I hypothesize that E1A might be involved in disrupting SUMO chain formation. (II) The second region that modulated PD is in the C-terminus of E1A. This second region targets the serine/threonine kinase DYRK1A. I show here that E1A binds DYRK1A and can stimulate its kinase activity. Finally we show that an E1A mutant that fails to bind DYRK1A is deficient in transforming cells in co-operation with E1B.;In mammalian and yeast systems, E1A has been shown to contain two regions that can independently induce transcription when fused to a heterologous DNA binding domain. Using 81 mutant yeast strains, I have evaluated the effect of deleting components of various transcriptional regulatory complexes on E1A dependent transcription. My analysis indicates that the two activation domains of E1A function via distinct mechanisms, identify new factors regulating E1A dependent transcription and suggests that yeast can serve as a valid model system for at least some aspects of E1A function.;Keywords. Adenovirus, E1A, Saccharomyces cerevisiae , Pseudohyphal growth/differentiation, UBC9, SUMO, DYRK1A, GLI1, Transformation, Transcription, Chromatin.