TelomereChromosomeCHROMOSOMECAPSCellTelomeresformprotectivecapsattheendsofchromosomes,andarebuiltfromarepeatingDNAsequenceconstructedbytheenzymetelomerase.TheDNAsequenceshownisfromtheTetrahymenatelomere.ThThDNDNAAhhiiffhth3’5’TTGGGGTTGGGGTTGGGGTTGGGGTTGGAACCCCAACCCCAACCCCAACCCCAACCNucleusLEFTTORIGHT:M.PROBST/APPHOTO;M.GROLL/APPHOTO;M.WILSONThreeUSscientistshavewontheNobelPrizeinPhysiologyorMedicinefordiscoveringthestructureofmolecularcapscalledtelomeresandworkingouthowtheyprotectchromo-somesfromdegradation.Theirdiscoveriesincellbiologyduringthe1980sand1990sopenednewavenuesofwork,inageingandincancerresearch,whicharestillhighlyactivetoday.Theprize,announcedon5October,issharedequallybetweenElizabethBlackburnattheUniversityofCalifornia,SanFrancisco,CarolGreideroftheJohnsHopkinsMedicalSchoolinBaltimore,Maryland,andJackSzostakatHarvardMedicalSchoolinBoston,Massachu-setts.Thethreehavealreadywonnumerousprizesfortheirwork,includingsharingoneofthe2006Laskerawards,oftenconsideredtobeaforerunneroftheNobelprize.Theirresearchrevealedafundamen-talaspectofhowDNA,packedintochromosomes,iscopiedinitsentiretybytheDNApolymeraseenzymeduringcelldivision.Theendsofthechromo-somesarecappedbytelomeres,longthoughttohaveaprotectivefunction(see‘Chromosomecaps’).Withoutthem,thechromosomeswouldbeshort-enedduringeachcelldivision,becauseDNAChromosomeprotectionscoopsNobelPrizeforphysiologyormedicineawardedforuncoveringroleoftelomeres.polymeraseisunabletocopytotheveryendofoneofthetwoDNAstrandsitisreplicating.Intheearly1980s,aftertheirfortuitousmeetingataGordonResearchConferencein1980,BlackburnandSzostakdiscoveredthattelomeresincludeaspecificDNAsequence.Firedupbythenoveltyofeachother’swork,theydevisedexperi-mentsthatseemedcrazyatthetime,eventothemselves.SzostaktookthetelomeresequencesthatBl