The genes , including the pef operon , PSLT026 , PSLT025 , PSLT024 , rsk , repA2 , srg ( srgA and srgB , SdiA-regulated gene ) , rck and srgC , are located in a region of about 11-kb in pSTLT2 ( McClelland et al. , 2001 ) ; however , in pOU1113 , the genes as well as the nucleotide sequences in this region ( 12 255 -- 23 104 bp ) were very different , occupied instead by a unique segment .