Proteins and Stuff PDF

**Proteins and stuff** **Chromatin and Epigenetics** - **Nucleosomes** - Made up of H2A, H2B, H3, AND H4 - H3-H4 dimers combine to form tetramers - Bind to two H2A-H2B dimers to form octamer - Binds 147bp of DNA - Joined by linker DNA of 38-53bp...

**Proteins and stuff** **Chromatin and Epigenetics** - **Nucleosomes** - Made up of H2A, H2B, H3, AND H4 - H3-H4 dimers combine to form tetramers - Bind to two H2A-H2B dimers to form octamer - Binds 147bp of DNA - Joined by linker DNA of 38-53bp - Histone variants and functions - H2A variants - H2AX - DNA repair and recombination - H2AZ - Gene expression - Chromosome segregation - macroH2A - Transcriptional repression - H3 variants - H3.3 - Transcriptional activation - CENP-A - Centromere function - Kinetochore assembly   - **Remodelling complexes** - SWI/SNF complex - Makes DNA accessible for transcription - Slides nucleosomes - Ejects nucleosomes - Alters nucleosome structure - Second most mutated gene across all cancers - INO80 complex - Nucleosome sliding - Histone exchange and replacement - Especially H2A.Z (good for transcription) - DNA damage repair - Important for making damaged DNA accessible to repair machinery - Replication stress response - Stabilises replication forks and prevents replication stress - Any condition that slows down or disrupts replication - ISWI (imitation switch) complexes - Involved in nucleosome spacing and assembly - Also used to reassemble nucleosomes after replication forks have passed - Examples - NURF - CHRAC - CHD (chromatin helicase DNA-binding) complexes - Play roles in nucleosome sliding and histone variant exchange - Some CHDs recognise methylated histones and modify chromatin in response to specific marks - Crucial for regulating chromatin structure in response to histone modifications - FACT (facilitates chromatin transcription) complex - Helps to disassemble and reassemble nucleosomes during transcription - Temporarily removes one of the H2A-H2B dimers from nucleosome - Allows RNA to transcribe through nucleosome   **Genetic Recombination**   +-----------------+-----------------+-----------------+-----------------+ | **Topic** | **Enzymes** | **Functions** | **Extra notes** | +=================+=================+=================+=================+ | Bacterial | RecA |   |   | | Recombination | | | | +-----------------+-----------------+-----------------+-----------------+ |   | RecB |   |   | +-----------------+-----------------+-----------------+-----------------+ |   | RecC |   |   | +-----------------+-----------------+-----------------+-----------------+ |   | RecD |   |   | +-----------------+-----------------+-----------------+-----------------+ | Holliday | RuvC |   |   | | Junctions (Pro) | | | | +-----------------+-----------------+-----------------+-----------------+ | Branch | RuvA |   |   | | Migration (Pro) | | | | +-----------------+-----------------+-----------------+-----------------+ |   | RuvB |   |   | +-----------------+-----------------+-----------------+-----------------+ |   | RecG |   | Also functions | | | | | at replication | | | | | forks | +-----------------+-----------------+-----------------+-----------------+ | Eukaryotic | RAD50 |   |   | | Recombination | | | | +-----------------+-----------------+-----------------+-----------------+ |   | XRS2 |   |   | +-----------------+-----------------+-----------------+-----------------+ |   | MRE11 |   |   | +-----------------+-----------------+-----------------+-----------------+ |   | Sae2 |   |   | +-----------------+-----------------+-----------------+-----------------+ |   | Tel1 |   |   | +-----------------+-----------------+-----------------+-----------------+ |   | RAD51 |   |   | +-----------------+-----------------+-----------------+-----------------+ |   | RAD52 |   |   | +-----------------+-----------------+-----------------+-----------------+ |   | BRAC2 |   | Mutation can | | | | | lead to | | | | | multiple forms | | | | | of cancer. | | | | | | | | | | - Cannot load | | | | | RAD51 onto | | | | | ssDNA | | | | | | | | | | - Disrupts HR | | | | | | | | | | - Cells rely | | | | | on | | | | | error-prone | | | | | repair | | | | | mechanisms | | | | | | | | | | - Non-hom | | | | | ologous | | | | | end | | | | | joining | | | | | (NHEJ) | | | | | | | | | | - Single- | | | | | strand | | | | | anneali | | | | | ng | | | | | (SSA) | +-----------------+-----------------+-----------------+-----------------+ | Branch |   |   |   | | migration (Euk) | | | | +-----------------+-----------------+-----------------+-----------------+ |   |   |   |   | +-----------------+-----------------+-----------------+-----------------+ |   |   |   |   | +-----------------+-----------------+-----------------+-----------------+