Construction and properties of a new insertion vector, pJDC9, that is protected by transcriptional terminators and useful for cloning of DNA from Streptococcus pneumoniae.

A new Escherichia coli plasmid cloning vector, pJDC9, was constructed by replacing the TcR determinant of pMB9 with the erythromycin-resistance ermB determinant and the lacZ alpha gene of pUC19. Efficient transcriptional terminator signals were positioned at both ends of lacZ alpha. Evidence is presented that protection of the vector by terminator signals enabled cloning of many fragments of DNA from Streptococcus pneumoniae that were unstable in vectors lacking such protection, including pBR322. At the pneumococcal mal locus, three promoter sites required such protection, while overexpression of the malX protein appeared to be lethal despite such protection.