MYB Family Transcription Factors

1. MYB Family Transcription Factors Jonathan Russell Rena Schweizer Mike Douglas Picture: Sequence specific binding of a transcription factor on DNA Picture: Sequence specific binding of a transcription factor on DNA

2. What is a Transcription Factor? Transcription factor � any protein other than RNA Polymerase that is required for transcription

3. MYB Family Myeloblast ---> MYB (came from first identified MYB which was in an avian oncogene) 203 identified MYB-family transcription factors Found in Eukaryotes

4. Our Genes Within the Myb Family

5. MYBFAMILY PHYLOGENY What is the Structure and Function of MYBs?

6. What is the Structure of MYB Proteins? All share a conserved MYB DNA-Binding Domain Up to three imperfect repeats (Helix-Turn-Helix structure) of ~53 AA each Repeats are R1, R2, R3 Tryptophan residues form a cluster in HTH structure (hydrophobic interactions) Repeats are R1, R2, R3 Tryptophan residues form a cluster in HTH structure (hydrophobic interactions)

7. What Motifs Do Mybs Employ? Helix-turn-Helix structures are crucial to sequence specificity HTH intercalates in major groove Recognition by C-terminal helix Recognize certain telomeric repeat sequences in DNA In relation to function, must recognize DNA in seq-specific manner C-terminal helix does recognition helix for DNA bindingRecognize certain telomeric repeat sequences in DNA In relation to function, must recognize DNA in seq-specific manner C-terminal helix does recognition helix for DNA binding

8. MYB Structure: R2R3 Sub Family Largest family characterized in plants Both R2 and R3 required for sequence-specific binding Some redundancy of amino acid sequence, but flexibility in recognition Over 1oo R2R3 sub myb proteins in Arabidopsis Although some redundancy of AA sequence among MYB genes, due to genes that have similar molecular functions but different biological phenotypes Some redundancy of amino acid sequence, but flexibility in recognition (which means that proteins very similar in their DNA-Binding domains control quite different target genes and therefore have quite distinct physiological functionsOver 1oo R2R3 sub myb proteins in Arabidopsis Although some redundancy of AA sequence among MYB genes, due to genes that have similar molecular functions but different biological phenotypes Some redundancy of amino acid sequence, but flexibility in recognition (which means that proteins very similar in their DNA-Binding domains control quite different target genes and therefore have quite distinct physiological functions

9. What are the functions of Plant MYB Proteins? Wide diversity of functions By no means fully characterized In general: regulate many aspects of plant metabolism and development But� Some bind telomeric sequences, structural Some are clearly transcription factors (from circadian clock to root hair formation)

10. Proposed Plant MYB Functions Vertebrates Cellular proliferation Expressed in actively dividing cells before differentiation Plants Control of secondary metabolism Regulation of cell morphogenesis Serving in signal transduction pathways responding to plant growth regulators

11. Specific MYB Functions Controlling Secondary Metabolism Phenylpropanoid metabolism (modifications of compounds derrived from phenylalinine) One branch resposible for the production of anthocyanins (major group of plant pigments) Regulating Cellular Morphogenesis In petunia, essential for developing the conical form of petal epidermal cells In Arabidopsis, essential for differentiation of hair cells in leaf and stem

12. The Future of MYB Experiments In order to characterize each MYB gene, mutation studies need to be performed This involves: knocking out specific genes and looking for resulting phenotypes�