Whether slo, the gene encoding streptolysin O (SLO), a streptococcal cytolysin, has its own
promoter or not is unsettled as yet. Present analyses demonstrate that slo is a member of an
operon covering the upper-stream nusG and nga (NADase) genes, from which transcription
of slo proceeds polycistronically, and major transcript is produced by readthrough from nga
promoter. Mutational conversion of the sixth nucleotide T at the putative− 10 region of
chromosomal nga gene into C caused a drastic decrease in both NADase and SLO activities …