Schematic representation of 5′→3′ exonuclease cleavage of a 5′-labeled (small black star) probe with a 3′-phosphate (grey circle) extension blocker. Schematic representation of 5′→3′ exonuclease cleavage of a 5′-labeled (small black star) probe with a 3′-phosphate (grey circle) extension blocker. After cleavage of the label from the probe by DNA polymerase (large black star), the small labeled fragments generated can be separated from the larger probe. Ad C. Fluit et al. Clin. Microbiol. Rev. 2001; doi:10.1128/CMR.14.4.836-871.2001