Cia peb xav txog cov haujlwm ntawm cov protein uas tsis yog histone, lawv qhov tseem ceeb rau lub cev. Lub ncauj lus no yog qhov txaus siab tshwj xeeb thiab tsim nyog kawm kom ntxaws.
Chromatin tseem ceeb proteins
Histone thiab cov protein tsis-histone yog txuas ncaj qha rau DNA. Nws lub luag hauj lwm nyob rau hauv muaj pes tsawg leeg ntawm interphase thiab mitotic chromosomes yog heev loj - khaws cia thiab faib cov ntaub ntawv genetic.
Thaum ua tiav cov haujlwm zoo li no, nws yuav tsum muaj lub hauv paus meej meej uas tso cai rau cov DNA ntev ntev los ua kom pom tseeb. Qhov kev ua no tso cai rau koj los tswj cov zaus ntawm RNA synthesis thiab DNA replication.
Nws cov concentration hauv interphase nucleus yog 100 mg / ml. Ib tug tsiaj txhu nucleus muaj txog 2 m ntawm DNA, nyob rau hauv ib tug kheej kheej nucleus nrog ib txoj kab uas hla ntawm 10 microns.
Protein pawg
Txawm hais tias muaj ntau haiv neeg, nws yog ib txwm ua rau ib leeg tawm ob pawg. Cov haujlwm ntawm histone thiab non-histone proteins muaj qee qhov sib txawv. Kwv yees li 80 feem pua ntawm tag nrho cov chromatin proteins yog histones. Lawv cuam tshuam nrog DNA los ntawm ionic thiab ntsev bonds.
Txawm tias muaj ntau npaum li cas, histones thiab non-histone proteins ntawm chromatinsawv cev los ntawm ntau yam tsis tseem ceeb ntawm cov proteins, eukaryotic hlwb muaj li tsib mus rau xya hom histone molecules.
Nonhistone proteins hauv chromosomes feem ntau yog tshwj xeeb. Lawv cuam tshuam nrog qee cov qauv ntawm DNA molecules.
Histone nta
Dab tsi yog cov haujlwm ntawm histone thiab cov protein uas tsis yog histone hauv chromosome? Histones khi nyob rau hauv daim ntawv ntawm ib tug molecular complex nrog DNA, lawv yog subunits ntawm xws li ib tug system.
Histones yog cov proteins yam ntxwv ntawm chromatin nkaus xwb. Lawv muaj qee yam zoo uas tso cai rau lawv ua haujlwm tshwj xeeb hauv cov kab mob. Cov no yog cov alkaline lossis cov proteins yooj yim, uas muaj cov ntsiab lus siab ntawm arginine thiab lysine. Vim yog cov nqi zoo ntawm cov amino pawg, electrostatic los yog ntsev daim ntawv cog lus yog tshwm sim nrog cov nqi sib txawv ntawm cov qauv phosphate ntawm DNA.
Daim ntawv cog lus no yog labile, nws yooj yim puas tsuaj, thiab kev sib cais rau hauv histones thiab DNA tshwm sim. Chromatin yog suav hais tias yog ib qho complex nucleic-protein complex, nyob rau hauv uas muaj ntau polymeric linear DNA molecules, raws li zoo raws li ib tug loj tus naj npawb ntawm histone molecules.
Properties
Histones yog cov protein me me raws li qhov hnyav molecular. Lawv muaj cov khoom zoo sib xws hauv txhua eukaryotes thiab pom los ntawm cov chav kawm zoo sib xws ntawm histones. Piv txwv li, hom H3 thiab H4 yog suav tias yog nplua nuj nyob rau hauv arginine, vim hais tias lawv muaj ib tug txaus tus nqi ntawm noCov amino acids.
Ntau yam ntawm histones
Cov histones no suav hais tias yog kev saib xyuas, txij li cov amino acid ib ntus hauv lawv zoo ib yam txawm nyob hauv hom nyob deb.
H2A thiab H2B raug suav hais tias yog cov protein ntau lysine. Cov khoom sib txawv hauv cov pab pawg no muaj qee qhov kev hloov pauv hauv cov qauv tseem ceeb, nrog rau cov kab ke ntawm cov amino acid residues.
Histone H1 yog ib chav kawm ntawm cov proteins uas cov amino acids tau teeb tsa hauv qhov sib xws.
Lawv qhia ntau qhov sib txawv tseem ceeb thiab kev sib txawv ntawm kev sib txawv. Ib qho tseem ceeb ntawm lysine yog suav tias yog cov cuab yeej dav dav, vim tias cov proteins no tuaj yeem sib cais los ntawm chromatin hauv cov kua ntsev ntsev.
Histones ntawm txhua chav kawm yog tus yam ntxwv los ntawm pawg faib ntawm cov amino acids tseem ceeb: arginine thiab lysine ntawm qhov kawg ntawm cov molecules.
H1 muaj qhov sib txawv N-lub ntsiab lus uas cuam tshuam nrog lwm cov histones, thiab C-terminus yog enriched nrog lysine, nws yog nws uas cuam tshuam nrog DNA.
Histone hloov kho tau ua tau thaum lub neej ntawm cov hlwb:
- methylation;
- acetylation.
Cov txheej txheem zoo li no ua rau muaj kev hloov pauv ntawm cov nqi zoo, lawv yog cov kev cuam tshuam rov qab. Thaum serine residues yog phosphorylated, ib qho kev tsis zoo tshaj plaws tshwm sim. Cov kev hloov kho no cuam tshuam rau cov khoom ntawm histones thiab lawv cov kev cuam tshuam nrog DNA. Piv txwv li, thaum histones yog acetylated, gene activation yog pom, thiab dephosphorylation ua rau decondensation thiab condensation.chromatin.
Synthesis nta
Cov txheej txheem tshwm sim hauv cytoplasm, tom qab ntawd nws raug thauj mus rau lub nucleus, khi rau DNA thaum nws rov ua dua hauv S-lub sijhawm. Tom qab qhov kawg ntawm DNA synthesis los ntawm lub cell, cov ntaub ntawv histone RNA decays nyob rau hauv ob peb feeb, cov txheej txheem synthesis nres.
Sib faib ua pab pawg
Muaj ntau hom tsis-histone proteins. Lawv faib ua tsib pawg yog muaj cai, nws yog raws li nyob rau hauv lub zoo sib xws. Tus naj npawb tseem ceeb ntawm cov khoom sib txawv tau raug txheeb xyuas hauv cov kab mob eukaryotic siab dua thiab qis dua.
Piv txwv li, tsis yog H1, tus yam ntxwv ntawm cov ntaub so ntswg ntawm cov kab mob hauv qis qis, pom histone H5, uas muaj ntau cov serine thiab arginine.
Tseem muaj cov xwm txheej cuam tshuam nrog ib feem lossis tsis tiav ntawm pawg histone hauv eukaryotes.
functionality
Cov protein zoo sib xws tau pom muaj nyob hauv cov kab mob, kab mob, mitochondria. Piv txwv li, hauv E. coli, cov proteins tau pom nyob rau hauv lub cell, cov amino acid muaj pes tsawg leeg uas zoo ib yam li histones.
Nonhistone chromatin proteins ua haujlwm tseem ceeb hauv cov kab mob muaj sia. Ua ntej kev txheeb xyuas cov nucleosomes, ob qhov kev xav tau siv los hais txog qhov tseem ceeb ntawm kev ua haujlwm, kev tswj hwm, thiab lub luag haujlwm ntawm cov proteins.
Nws tau pom tias thaum RNA polymerase ntxiv rau cov chromatin cais, tau txais ib daim qauv rau cov txheej txheem sau ntawv. Tab sis nws txoj haujlwm yog kwv yeestsuas yog 10 feem pua ntawm qhov ntawd rau DNA ntshiab. Nws nce nrog kev tshem tawm ntawm pawg histone, thiab hauv lawv qhov tsis muaj nws yog tus nqi siab tshaj plaws.
Qhov no qhia tau tias tag nrho cov ntsiab lus ntawm histones tso cai rau koj los tswj cov txheej txheem sau ntawv. Kev hloov pauv zoo thiab ntau npaum li cas hauv histones cuam tshuam rau kev ua haujlwm ntawm chromatin, qib ntawm nws cov compactness.
Cov lus nug ntawm qhov tshwj xeeb ntawm kev tswj hwm tus yam ntxwv ntawm histones thaum lub sijhawm sib txuas ntawm mRNAs tshwj xeeb hauv cov hlwb sib txawv tsis tau kawm tiav.
Nrog rau qhov sib ntxiv ntawm ib feem histone rau cov kev daws teeb meem uas muaj DNA ntshiab, nag lossis daus tau pom nyob rau hauv daim ntawv ntawm DNP complex. Thaum cov histones raug tshem tawm los ntawm cov tshuaj chromatin, ib qho kev hloov pauv tiav rau hauv lub hauv paus soluble tshwm sim.
Lub luag haujlwm ntawm cov protein uas tsis yog histone tsis txwv rau kev tsim cov molecules, lawv muaj ntau txoj hauv kev thiab ntau yam.
Qhov tseem ceeb ntawm nucleosomes
Hauv thawj cov kev tshawb fawb electromicroscopic thiab biochemical, nws tau ua pov thawj tias muaj cov qauv filamentous hauv DPN kev npaj, txoj kab uas hla ntawm 5-50 nm. Nrog rau kev txhim kho cov tswv yim hais txog cov qauv ntawm cov protein molecules, nws tau pom tias muaj kev sib raug zoo ntawm txoj kab uas hla ntawm chromatin fibril thiab cov txheej txheem ntawm kev cais tshuaj.
Ntawm ntu nyias ntawm mitotic chromosomes thiab interphase nuclei, tom qab kuaj pom nrog glutaraldehyde, chromated fibrils tau pom, qhov tuab ntawm 30 nm.
Fibrils muaj qhov sib xwschromatin nyob rau hauv cov ntaub ntawv ntawm lub cev fixation ntawm lawv cov nuclei: thaum lub sij hawm khov, chipping, noj replicas los ntawm kev npaj zoo sib xws.
Cov proteins uas tsis yog histone ntawm chromatin tau pom nyob rau hauv ob txoj kev sib txawv los ntawm chromatin particle nucleosomes.
Kev Tshawb Fawb
Thaum chromatin npaj tau tso rau ntawm lub substrate rau electron microscopy nyob rau hauv alkaline tej yam kev mob nrog insignificant ionic zog, chromatin strands zoo li cov hlaws dai tau txais. Lawv qhov loj me tsis pub tshaj 10 nm, thiab cov globules sib cuam tshuam los ntawm DNA ntu, qhov ntev tsis tshaj 20 nm. Hauv kev soj ntsuam, nws muaj peev xwm tsim kom muaj kev sib txuas ntawm cov qauv ntawm DNA thiab cov khoom lwj.
Npaj ntaub ntawv
Non-histone proteins tsim txog nees nkaum feem pua ntawm cov protein chromatin. Lawv yog cov proteins (tshwj tsis yog cov uas tau zais los ntawm chromosomes). Cov proteins uas tsis yog-histone yog ib pawg ntawm cov proteins uas sib txawv ntawm ib leeg tsis yog hauv cov khoom xwb, tab sis kuj tseem ua haujlwm tseem ceeb.
Feem ntau ntawm lawv yog hais txog cov protein matrix nuclear, uas pom muaj ob qho tib si hauv cov ntsiab lus ntawm interphase nuclei thiab hauv mitotic chromosomes.
Cov proteins uas tsis yog histone tuaj yeem suav nrog txog 450 tus neeg polymers nrog qhov hnyav molecular sib txawv. Qee tus ntawm lawv yog soluble hauv dej, thaum lwm tus yog soluble hauv acidic daws. Vim qhov tsis sib haum xeeb ntawm kev sib txuas nrog cov chromatin ntawm kev sib cais tsis tu ncua nyob rau hauv lub xub ntiag ntawm denaturing agents, muaj teeb meem loj nrog rau kev faib thiab kev piav qhia ntawm cov protein molecules.
Nonhistone cov proteins yog cov tswj hwm cov khoom siv polymers,stimulating transcription. Kuj tseem muaj cov inhibitors ntawm cov txheej txheem no uas khi rau hauv ib ntu ntawm DNA.
Nonhistone cov protein kuj tseem tuaj yeem suav nrog cov enzymes koom nrog hauv cov metabolism ntawm nucleic acids: RNA thiab DNA methylases, DNases, polymerases, chromatin proteins.
Ib puag ncig ntawm ntau cov sib xyaw polymeric zoo sib xws yog suav tias yog cov kev tshawb fawb tshaj plaws uas tsis yog histone proteins nrog kev txav mus los. Lawv yog cov yam ntxwv los ntawm zoo electrophoretic mobility, extraction nyob rau hauv ib tug tov ntawm ntsev.
HMG proteins tuaj nyob rau hauv plaub hom:
- HMG-2 (m.w.=26,000),
- HMG-1 (m.w.=25,500),
- HMG-17 (m.w.=9247),
- HMG-14 (m.w.=100,000).
Ib lub cell nyob ntawm cov qauv no tsis muaj ntau tshaj 5% ntawm tag nrho cov nyiaj histones. Lawv tshwj xeeb tshaj yog nyob rau hauv active chromatin.
HMG-2 thiab HMG-1 cov proteins tsis suav nrog hauv nucleosomes, lawv tsuas yog khi rau txuas DNA tawg.
Proteins HMG-14 thiab HMG-17 tuaj yeem khi rau lub plawv zoo li polymers ntawm nucleosomes, uas ua rau muaj kev hloov pauv hauv qib sib dhos ntawm DNP fibrils, lawv yuav nkag tau ntau dua rau cov tshuaj tiv thaiv nrog RNA polymerase. Nyob rau hauv cov xwm txheej zoo li no, HMG proteins ua lub luag haujlwm ntawm kev tswj hwm ntawm kev ua haujlwm ntawm kev hloov pauv. Nws tau pom tias cov chromatin feem, uas muaj kev nkag siab zoo rau DNase I, yog saturated nrog HMG proteins.
Zoo kawg
Qib peb ntawm cov txheej txheem ntawm chromatin yog lub voj ntawm DNA. Nyob rau hauv cov chav kawm ntawm kev tshawb fawb, nws tau pom tias tsuas yogdeciphering lub hauv paus ntsiab lus ntawm chromosomal elementary Cheebtsam, nws yog ib qhov nyuaj kom tau ib tug tiav daim duab ntawm chromosomes nyob rau hauv mitosis, nyob rau hauv interphase.
DNA densification los ntawm 40 zaug tau txais vim qhov siab tshaj plaws spiralization. Qhov no tsis txaus kom tau txais lub tswv yim tiag tiag ntawm qhov loj thiab cov yam ntxwv ntawm chromosomes. Nws tuaj yeem txiav txim siab qhov tseeb tias yuav tsum muaj qib siab dua ntawm DNA sib dhos, nrog kev pab cuam uas nws yuav ua tau kom tsis meej pem chromosomes.
Cov kws tshawb fawb tau tshawb pom cov qib zoo sib xws ntawm cov koom haum chromatin vim nws cov khoom tsim tawm decondensation. Nyob rau hauv cov xwm txheej zoo li no, cov proteins tshwj xeeb yuav khi rau qee ntu ntawm DNA uas muaj cov thawj hauv cov chaw koom nrog.
Lub hauv paus ntsiab lus ntawm DNA lub voj ntim khoom kuj tau pom nyob rau hauv eukaryotic hlwb.
Piv txwv li, yog tias cov nuclei cais tau kho nrog kev daws ntawm cov ntsev ntsev, kev ncaj ncees ntawm cov nucleus yuav raug khaws cia. Cov qauv no hu ua nucleotide. Nws qhov chaw nruab nrab suav nrog tus lej tseem ceeb ntawm cov DNA kaw, qhov nruab nrab qhov loj yog 60 kb.
Nrog kev npaj cais ntawm chromomeres, ua raws li kev rho tawm ntawm cov histones los ntawm lawv, cov qauv zoo li rosette yuav pom nyob rau hauv lub tshuab ntsuas hluav taws xob. Tus naj npawb ntawm loops nyob rau hauv ib lub qhov (socket) yog los ntawm 15 mus rau 80, tag nrho ntev ntawm DNA mus txog 50 microns.
Cov tswv yim hais txog cov qauv thiab cov yam ntxwv tseem ceeb ntawm cov protein molecules, tau txais hauv chav kawm ntawm kev sim ua haujlwm, tso cai rau cov kws tshawb fawb los tsim tshuaj, tsim tshiabtxoj kev zoo tiv thaiv kab mob caj ces.
