plasmid dna isolation procedureprinciple of plasmid dna isolationisolation of plasmid dna from bacteriaplasmid dna isolation methodsisolation of genomic and plasmid dnaplasmid dna preparationpurifying plasmid dnaplasmid dna extractionisolation of vector dnaplasmid isolation stepsplasmid dna purification protocolplasmid dna extraction principle