Fig 4.

Core cas genes are organized in two operon structures. Polycistronic mRNAs cascis (TTX_1245 to TTX_1248) and cascade (TTX_1250 to TTX_1255) were identified by amplification of cDNA and the products were separated on agarose gels. PCR products (lanes a to f, marked by asterisks) of overlapping gene regions correlated to the calculated length (primer sets see Table S2 in the supplemental material). M, DNA ladder. As a negative control, primer sets binding outside of the polycistronic mRNA were used (data not shown).