Eur.J.Biochem.251,9218(1998)FEBS1998ReviewChromatinandtranscriptionHowtranscriptionfactorsbattlewitharepressivechromatinenvironmentPhilipD.GREGORYandWolframHÖRZAdolf-Butenandt-InstitutfürPhysiologischeChemie,UniversitätMünchen,München,Germany(Received4August/13October1997)2EJB971109/0Thelastyearhasseenmuchprogressinourunderstandingofchromatinandtranscription.Transcrip-tionallyactivechromatinhaslongbeencorrelatedwithahigherlevelofhistoneacetlyation.Thediscoveryofanuclearhistoneacetyltransferaseactivityencodedbyfactorswitharoleintranscriptionraisesthepossibilitythatthecellisabletodynamicallymodulatethe(local)levelofhistoneacteylation,switchingchromatintemplatesfrominactivetotranscriptionallyactivestates.Furthermore,histoneacetylationstateshaveshowntoplayaroleindeterminingtheefficacyoftranscriptionallysilencedchromatininbothyeastandDrosophila.Theadvancesinourknowledgeregardingtheroleoftheorigin-recognitioncomplexintheestablishmentofsilencing,andtherequirementforalocallyconcentratedzoneofthesilenceinforma-tionregulatorproteinsinthenucleushasprovidedinsightsintothecomplexarchitectureofsilencedchromatin.Thegoalofunderstandingthemechanismsbywhichthecellisableto‘open’repressivechromatinstructureshaspromptedthediscoveryofmultiplechromatinremodellingactivites.Theselargeproteincomplexesidentifiedfromorganismsasdiverseasyeast,mouse,flyandmandemonstratetheubiquityandfundamentalimportanceoftheabilitytoperturbthestructureofchromatinallowingtran-scriptionofthedesiredgenes.Thesedataprovidethelatestandpotentiallymostsignificantdemonstrationoftheimportanceofthenucleosomeintheregulationoftranscription.Keywords:chromatinremodeling;nucleosome;transcriptionalregulation;histoneacetylation;telomere;silencing;positioneffect;SWI/SNF;GCN5;RPD3.Theregulationofgeneexpressionisofparamountimpor-Silencingandposition-effectvariegation(PEV)tancetoallaspectsofcellbiology.GenesfunctioninadynamiccomplexofDNAandproteintermedchromatin,whichwasonceTheeukaryoticchromosomeis