Figure 1: Schematic map of the SpnD39III locus and of the six alternative hsdS genes.
From: A random six-phase switch regulates pneumococcal virulence via global epigenetic changes
In strain D39, the Type I RM system SpnD39III locus (upper row from right to left) includes hsdR (locus_tag SPD_0455; GenBank protein database accession code ABJ53942; REBASE SpnD39ORF782P), hsdM (SPD_0454; ABJ54850; M.SpnD39ORF454P) and hsdS (SPD_0453; ABJ53819; S3.SpnD39ORF454P), a Cre recombinase (SPD_0452; ABJ54057), a truncated hsdS′ gene with only one variable domain (SPD_0450; ABJ55250; S2.SpnD39ORF454P) and a further truncated hsdS′′ gene with two variable domains (SPD_0451; ABJ54176; S1.SpnD39ORF454P). Three series of inverted repeats (IR1 to IR3) allow for recombination. These rearrangements, exemplified by crosses between the IRs, allow formation of six different variant hsdS alleles encoding different HsdS proteins SpnD39IIIA-F. Inverted repeats are of 85 (IR1, striped), 333 (IR2, dotted) and 15 bp (IR3). The six recombinant s.spnD39IIIA-F alleles (Genbank nucleotide database accession codes KJ955483, KJ955484, KJ955485, KJ955486, KJ398403 and KJ398404) are shown below with their TRDs numbered according to Table 1.
