EMBL3 and EMBL4 - Replacement Vectors, Stuffer, Genomic Libraries, Replacement Vectors

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	EMBL3 and EMBL4 - Replacement Vectors - EMBL3 and EMBL4 two vectors that are designed so that a central non essential part of 44 kb long phage can be replaced by a foreign DNA. Cleavage of the phage with an appropriate enzyme generates three fragments (left arm, right arm and a central fragment called stuffer). The central fragment representing 40% of the phage genome is nonessential for propagation of the phage and can be replaced by foreign DNA that may be as long as 20-23 kb.
Non recombinant DNA resulting from fusion of left arm and right arm will give a DNA that is too small for packaging, so that there is automatic selection against non-recombinant phages. EMBL3 and EMBL4 are two such replacement vectors used for preparing genomic libraries in eukaryotes with cloned fragments, 15-25 kb in size. The two vectors have polylinkers with reverse orders of restriction sites with respect to each other.