GenomeAnalysis Group, Deutsches Krebsforschungszentrum,

Totesttheeffectiveness ofordering shotgun DNAtemplates prior tosequenceanalysis, the450kbleft arm ofyeastchromosomeXIIwas randomly subcloned into aphagemid vector. Clones wereordered by hybridisation toan averagemap density ofone new insert every125bp and are currently usedfor sequencing thechromosomal fragment. An 11.5kb overlap between thetemplate map andaDNAfragment thathadbeensequenced earlier allowed an independentevaluation ofthestrategy's effectiveness. Tothis end,clones wereselected fromthemap andtag-sequencedfromeither end,thuscomparing themap position withtheactual location within the11.5kb.Of 65selected clones, takenmostly atrandomfromatotal of423,58mappedon averageabouta quarter ofa clonelength aroundtheir predicted position, withthe other sevenbeing between 0.6and1.5clonelength off. 75-86sequencing reactions on clonesselected from themap wouldhavebeensufficient forcompletely sequencing bothstrands ofthe11.5kbfragment. The resuits demonstrate theefficacy ofsuchtemplate sorting, considerably assisting sequencing atrelativelylittle costonthemappinglevel.