pBBR RESO is a broad-host-range promoter cloning vector. It was derived from pBBR1MCS, which itself is a modification of the broad-host-range plasmid pBBR1CM. In contrast to other known broad-host-range vectors, pBBR RESO is maintained at a medium copy number and has a reasonable size of about 6.8 kb. It stably replicates in any Gram-negative bacterium studied and is therefore ideal for the isolation and genetic analysis of DNA sequences with promoter activity in the homologous organism. The reporter system used employs the resolvase-mediated excision of a kanamycin (Kan)-resistance gene flanked by two res sequences. Cloning an active promoter results in Kan-sensitive clones.