MBB331_Week10-Fall-2011

Myodmyod homodimer myodmyod homodimer active active

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Unformatted text preview: OTIFS HELIX­ A. B. Lewin Genes VII 2000 Oxford University Press • Heterodimers between Heterodimers bHLH & nonbasic HLH nonbasic proteins block DNA binding binding • ie. MyoD/MyoD homodimer MyoD/MyoD homodimer ---> active active • MyoD/Id heterodimer ---> MyoD/Id heterodimer 10 inactive inactive CLASSES OF HLH PROTEINS CLASSES OF HLH PROTEINS • bHLH proteins: E12 & E47 (Ig enhancer-binding bHLH factors); MyoD, myogenin, & Myf-5 (myogenesis/muscle formation); Myc proto-oncogene (growth reg); da & AC-S (CNS development in Drosophila) Drosophila • Class A: ubiquitously expressed - E12/E47 & da • Class B: tissue-specific - MyoD & AC-S • Combinatorial associations between HLH proteins Combinatorial enable complex regulations ie. various combinations of ie various MyoD/E12/E47/Id regulate muscle cell formation MyoD/E12/E47/Id 11 TRANSCRIPTION FACTOR FAMILIES: HELIX­LOOP­HELIX (HLH) MOTIFS HELIX­ -dimers of bHLH proteins vary in their ability to bind DNA and dimer formation introduces a degree of regulation eg. E12/E47 heterodimer binds DNA strongly but E12 homodimer binds poorly -in Drosophila, the gene emc is involved in establishing pattern of adult sensory organs, and functions by repressing activity of genes such as da (daughterless) and achaete-scute complex (AC-S) 12 Lewin Genes VII 2000 Oxford University Press TRANSCRIPTION FACTOR FAMILIES: HELIX­LOOP­HELIX (HLH) MOTIFS HELIX­ -if da and AC-S not suppressed too many cells a...
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