Genetic Organization of Plasmid ColJs, Encoding Colicin Js Activity, Immunity, and Release Genes

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Abstract
The 5.2-kb ColJs plasmid of a colicinogenic strain of Shigella sonnei (colicin type 7) was isolated and sequenced. pColJs was partly homologous to pColE1 and to pesticin-encoding plasmid pPCP1, mainly in the rep , mob , and cer regions. A 1.2-kb unique region of pColJs showed significantly different G+C content (34%) compared to the rest of pColJs (53%). Within the unique region, seven open reading frames (ORFs) were identified. ORF94 was shown to code for colicin Js activity ( cja ), a 94-amino-acid polypeptide (molecular mass, 10.4 kDa); ORF129 ( cji ) was shown to code for the 129-amino-acid colicin Js immunity protein (molecular mass, 14.3 kDa); and ORF65 was shown to be involved in colicin Js release by producer bacteria ( cjl ) coding for a 65-amino-acid polypeptide (molecular mass, 7.5 kDa). In contrast to the gene order in other colicin operons, the cjl gene was found upstream from cja . Moreover, the promoter upstream from cjl was similar to promoters described upstream from several colicin activity genes. The cji gene was found to be located downstream from cja with a transcription polarity opposite to that of the cjl and cja genes. The cja , cji , and cjl genes were not similar to other known colicin genes. Colicin Js was purified as an inactive fusion protein with an N-terminal histidine tag. Activity of the purified fusion form of colicin Js was restored after cleavage of the amino acids fused to the colicin Js N terminus.

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