BIOL 300 Lecture Notes - Lecture 7: Histone H3, Transcription Factor Ii D, Conformational Change
5 Mar 2018
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Lecture 7 mechanism of transcriptional regulation by co-activators cont"d. Until early 2000, histone methylation has been considered to be a permanent modification: two possible mechanisms of turnover, 1. Histone tail clipping or replacement by an unmodified or variant form of histones: 2. Histone methylation: histone tail lysine methylations are regulated by histone methyltransferases (hmts) and demethylases recruited to trans-factor activation/repression domains, chromodomain: containing proteins recognize histone tail methylaitons associated with closed chromatin (ex: H3k9, h3k27: one of these chromodomain proteins is hp1 (heterochromatin associated protein 1, in addition to binding to k9 methylated histones, This oligomerization condenses h3k9 methylated chromatin into a tightly-packed heterochromatin structure: moreover, hp1 recruits h3k9 methyltransferases. Positive feedforward system which leads to heterchromatin spreading: some hmts themselves contain chromodomains, positive feedforward system allows heterochromatin to persist through dna replication (epigenetic: changes in inheritable cellular phenotype that does not involve changes in dna sequences)
