The pGEM-7Zf(+) and pGEM-7Zf(-) Vectors are derivatives of the pGEM-3Zf(+) Vector and contain the origin of replication of the filamentous phage f1. These plasmids serve as standard cloning vectors, as templates for in vitro transcription and can be used for the production of circular ssDNA. These plasmids contain SP6 and T7 RNA polymerase promoters flanking a region of multiple cloning sites within the alpha-peptide coding region of beta-galactosidase. Insertional inactivation of the alpha-peptide allows recombinant clones to be identified directly by color screening on indicator plates when using appropriate E. coli strains (e.g., JM109). The multiple cloning region is unique and includes restriction sites for ApaI, AatII, SphI, XbaI, XhoI, EcoRI, KpnI, SmaI, ClaI, HindIII, BamHI, SacI, BstXI and NsiI. This arrangement is designed specifically for generating unidirectional deletions with the Erase-a-Base System. pGEM-7Zf(+) and pGEM-7Zf(-) Vectors are identical except for the orientation of the f1 origin.