Histone Modifications & Epigenetics

4 Pages
Unlock Document

Biochemistry & Molecular Bio.
David Gross

Feb 21 Notes • Histone mods can spread o acetylation occurs during transcription and is removed after o methylation occurs after transcription and prevents expression • Code-reader complex o scaffold protein holds protein modules that bind to specific histone mods on nucleosome o it then attracts other components such as a protein complex w/ catalytic activities & additional binding sites o this leads to gene expression, gene silencing, or other biological functions • Histone mods can spread o code-reader proteins can recruit code-writer proteins o if the mark that is read to recruit the code-reader protein is the same as the mark that is written by the code-writer protein, the process can occur again and spread across nucleosomes • Code-writer complexes o association of reader-writer complexes w/ chromatin remodeling complexes can drive condensation of chromatin • Barrier proteins o prevent overspreading of heterochromatin (silenced regions) o histone acetylases can act as barrier proteins & prevent spreading of methylation by reader-writer complexes o can either be a physical barrier to methylation or modify the histones in a competitive way • Many histone subtypes o variation for each core histone except H4 exist  these contribute to the histone code o there can be different types of N-terminal tail sequences & changes in core histone-folds o Ex.  H3.3 – causes transcriptional activation  CENP-A(H3 mod) – centromere function & kinetochore assembly  H2AX – DNArepair & recombination  H2AZ – gene expression, chromosome segregation  macroH2A(H2Amod) – transcriptional repression, X-chromosome inactivation • Remodeling complexes o useARP hydrolysis to alter chromatin composition o w/ histone chaperones can exchange histone components or even entire core o chaperones keep histones soluble until recruited into nucleosome • Histone variants cause different mechanisms to occur o CENP-A(H3 mod) helps recruit kinetochore components  the mod allows kinetochore components to attach to different recruited proteins o in yeast a specific 125 bp sequence sufficient to generate centromere (enough to recruit 1 histone octomer) • Centromeres o centromeres can extend over 1000kb & don’t need to contain specific centromeric sequence (flies & humans example)  instead simple repeat regions where centromeres form (alpha satellite DNA) o in this case centromeres defined more by protein composition than DNAsequence  regions of alpha satellite DNAcan exist w/o centromeric proteins  neocentromeres can form @ non-alpha satellite regions (rare) o longer centromeres consist of repeating regions w/ CENP-Ahistones & dimethylated normal H3’s (@ K4) • Heterochromatin o pericentric heterochromatin are compacted chromatin on the edge of the heterochromatic region (outli
More Less

Related notes for BIOCHEM 524

Log In


Join OneClass

Access over 10 million pages of study
documents for 1.3 million courses.

Sign up

Join to view


By registering, I agree to the Terms and Privacy Policies
Already have an account?
Just a few more details

So we can recommend you notes for your school.

Reset Password

Please enter below the email address you registered with and we will send you a link to reset your password.

Add your courses

Get notes from the top students in your class.