Lecture 12. Vertebrate genetic models and screens • • • • Zebrafish genetic model • • • • • • • • • • • • • • • • • • • • • • • • • • • Eddy De Robertis proposed an Urbilaterian shared ancestor. Ur = original • slide25 Image result for pilsner urquell • • • • • • Reading • • • • • • • • Lecture 12. Early genetic screens and vertebrate genetic screens • • • • • • • • • • • • • • • • A classical model of inducible gene expression in a eukaryote. •GAL1 galactokinase (mutant allele is gal1) •GAL2 galactose permease •GAL7 galactose uridyl transferase •GAL10 galactose-glucose epimerase • •GAL4 positive regulator (mutant is gal4) •GAL80 negative regulator (mutant is gal80) Yeast GAL genes are positively regulated at the level of transcription activation. •A gal4, gal80 double mutant fails to induce expression of galactose enzymes. (gal4 mutation is epistatic to gal80) • •Interpretation is that GAL4 targets the structural genes to activate transcription. • •GAL80 interacts with GAL4 to control its activity. Mechanism of transcription activation of the yeast GAL genes. • See the source image See the source image ONPG hydrolysis by cells gives a soluble blue product for spectrophotometric measurement of lacZ (β-galactosidase ) activity units GAL1-lacZ and GAL10-lacZ fusions used for deletion analysis. lacZ (β-galactosidase)) plate tests and liquid culture assays for beta-gal activity units. See the source image Deletion analysis of yeast GAL1 upstream region defined an Upstream Activating Site (UASG). • GAL1-lacZ and GAL10-lacZ fusions used for deletion analysis. UASG had many properties of the Enhancer defined in SV40. Four copies of a nearly symmetric 17 bp GAL4 site.