【英语翻译NrrADirectlyRegulatesExpressionofhetRduringHeterocystDifferentiationintheCyanobacteriumAnabaenasp.StrainPCC71201Heterocystsareterminallydifferentiatedcellsofcyanobacteriathatarecapableoffixingatmosphericnitrogen】

　　英语翻译

　　NrrADirectlyRegulatesExpressionofhetRduringHeterocyst

　　DifferentiationintheCyanobacteriumAnabaenasp.StrainPCC71201

　　Heterocystsareterminallydifferentiatedcellsofcyanobacteria

　　thatarecapableoffixingatmosphericnitrogen.Upon

　　limitationofcombinednitrogeninthemedium,particularvegetative

　　cellschangetheirformintoheterocystswitharegular

　　spacingof10to15cells(10,12,29).Inthefilamentouscyanobacterium

　　Anabaenasp.strainPCC7120,about10%of

　　genesonthechromosomeareestimatedtobeupregulated

　　duringheterocystdevelopment(6,7).Heterocystsmarkedly

　　differfromvegetativecellsinphysiologicalandmorphological

　　aspects(30).Heterocystdevelopmentprovidesanexcellent

　　modelforstudyingcelldifferentiationandmulticellularpattern

　　formation.

　　ThehetRgeneisamastergenethatregulatesheterocyst

　　differentiation.WhilemutationinthehetRgeneblocksearly

　　stepsindifferentiation,extracopiesofhetRresultintheformation

　　ofmultiplecontiguousheterocysts(Mchphenotype)

　　undernitrogen-depletedconditions(4).ExpressionofhetR

　　fromthepetEpromoter,whichisregulatedbycopper,induces

　　heterocystdifferentiationirrespectiveofcellularnitrogenstatus

　　(5).ThelevelofthehetRtranscriptsincreasesshortlyafter

　　nitrogendeprivation,anditsexpressionislocalizedtoheterocysts

　　(2).TheupregulationofhetRdependsonntcA(9).

　　ThentcAgene,whichisrequiredforheterocystdevelopment

　　(9,28),encodesatranscriptionalregulatorthatgloballycontrols

　　nitrogenmetabolismincyanobacteria(19,27).TheNtcA

　　protein,belongingtothecyclicAMPreceptorproteinfamilyof

　　bacterialregulators,bindstopromoterregionscontainingthe

　　sequencesignatureGTAN8TAC(12),andaneight-basepalindromic

　　sequence,TGTAN8TACA,isshowntobetheoptimal

　　NtcA-bindingsequencebyinvitroselection(15).The

　　DNA-bindingactivityofNtcAisenhan