Fig 8. Frequency distribution of HT_Spy1336-7 size variants in the emm28 strains studied and effect on Spy1336/R28 and Spy1337 transcript levels.

Addition or deletion of one T nucleotide in the homopolymeric tract results in a statistically significant change in transcript levels for Spy1336/R28 and Spy1337 and a consequent effect on virulence. There are three transcript states based on number of T residues in the HT_Spy1336-7 region. In state 1 (9Ts, left), there are essentially no detectable transcripts of Spy1336/R28 and Spy1337. State 2 (10Ts, center) is characterized by increased transcripts of these two genes, and state 3 (11Ts, right) results in further increase in transcripts of Spy1336/R28 and Spy1337.