Allow "ghost" plasmids in cloning

[manulera]

Especially for allele description in papers where the plasmid is given by name but sequence can't be found, if the plasmid has only been used to clone a fragment, and then clone it out.

[manulera]

Example from https://doi.org/10.1242/jcs.001115

The cdc8-AS allele was created by PCR using primers oDM109 (5′-CATATGGCTAGCATGG-ATAAGCTTAGAGAGAAAAT-3′) and oDM112, cloned into pTOPO2.1 and sequenced (creating pTOPOcdc8-AS). The cdc8+ and cdc8-AS alleles were subsequently cloned into the pJC20 bacterial T7 expression vector.