Maps of the retrofitting vectors, BACs and the retrofitted BACs a) pRetro vectors; pRetroNeo, pRetroNeoLuc, pRetroNeoLucOE and pRetroNeoOE. Selected restriction sites are indicated. b) Retrofitting of standard BACs; pBeloBAC11, pBeloBAC11 retrofitted with pRetroNeo (pBeloBACRetroNeo), pBACe3.6, and pBACe3.6 retrofitted with pRetroNeoLucOE (pBACe3.6RetroNeoLucOE). NotI sites are indicated. c) Retrofitting of specific BACs; BACLucA, BACLucARetroNeoOE, BACGFPNeoOE, and BACGFPNeoOERetroNeoLuc. NotI sites are indicated. The following elements are labelled; spectinomycin resistance gene (SpR), gamma origin from the R6K plasmid (R6K ori), loxP site (LoxP), G418 resistance cassette (NeoR), luciferase expression cassette (Luc), oriP from Epstein Barr virus (OriP), EBNA-1 gene from Epstein Barr virus (EBNA-1), chloramphenicol resistance gene (CmR), F1 origin from the F factor (F1 ori), SacBII gene (SacBII), lacZ gene (LacZ) and EGFP expression cassette (eGFP).