Cleave with restriction ≈ enzyme of a Promoter S RN Cloned cDNA Exonuclease Bamhl Cleave d、Awth 0 min Psti and BanH 1 min 2 min 5 GATCC CTGCA mln 3′G 4 min DNA ligase -Oligonuclcotide linker ExonucleaseⅢ Extent of 5 GATCC : cTGA deletion controlled ATCC CTGA by time G Cut of B and C B Single stranded DNAl Nuclease SI of digestion solate 5Sgene fragments C Blunt ends C Ligate into new vector G Transform F coli Ligate linker DNAS promoter- Rightward deletion mutants intact Linker CDNA remaining fter deletion 图8-3系列缺失突变法