¹G.K. Scryabin Institute of Biochemistry and Physiology of Microorganisms RAS, Pushchino Scientific Center for Biological Research of the Russian Academy of Sciences, Pushchino, Russia
²ITMO University, Saint-Petersburg, Russia

Abstract. The paper discusses the distribution of the hlyII and hlyIIR genes, which encode hemolysin II and its transcriptional regulator, respectively, among genomes of Bacillus cereus sensu lato. Along with the full-length toxin, the presence of truncated forms of HlyII is described. Bioinformatic analysis of 4,962 genomes revealed that 1,408 genomes contained intact both hlyII and hlyIIR genes, 584 genomes contained hlyIIR and truncated forms of hlyII, and 2,699 genomes (54.4 %) lacked both genes. In 84 % of B. anthracis genomes (419 out of 496), the full-length hlyIIR gene was identified, whereas the hlyII gene harbored a mutation disrupting the reading frame, which was restored in the 3’-region of the gene. Consequently, these strains are capable of synthesizing N-terminally truncated variants of the HlyII protein. No instances of the hlyII gene (either full-length or truncated) occurring in the absence of the hlyIIR gene were identified among B. cereus sensu lato genomes. Analysis of aligned operator regions recognized by the HlyIIR revealed mirror symmetry and strict complementarity within the sequence. The central region of the sequence (nucleotides 21–25) is the most variable, where the palindromic principle may be violated. The sequence TTTAAA, repeated four times in the operator, is the most conserved. Analysis of DNA areas upstream of the hlyII gene identified conserved and variable regions critical for DNA-protein interactions and potentially involved in the regulation of the hlyII gene.

Key words: pathogenicity factors, hemolysin II, transcription regulation, operator, DNA-protein recognition, HlyIIR, Fur, ResDE