Comparison of the genetic organization of PAI I536 to PAI IV536. Known or putative ORFs are grouped according to the following characteristics: blue, functional, known ORFs; green, truncated ORFs with a start codon and a stop codon; grey, as-yet-unidentified ORFs without homology on the DNA level. Nonfunctional ORFs (e.g., due to internal stop codons or frameshifts) are indicated by hatched symbols. ORF numbers are indicated below the corresponding ORF symbols. Functional or truncated tRNA-encoding genes are marked in red. Direct repeat (DR) structures flanking PAIs are indicated. Thick black lines below the PAIs represent regions of PAI I536 PAI IV536 which were detected by PCR. Several PAI-specific PCRs were grouped into PAI regions.