Fig 1.

Schematic description of the substrates used for assaying the removal of Tf1 SP or PPT substrates. The substrates were prepared as described in detail in Materials and Methods. The 11-nt-long RNA segments with sequences of either the Tf1 SP or PPT were 5′ end labeled with ³²P. The labeled RNA was then annealed to Tf1-derived DNA segments with the appropriate 3′ ends that match either the SP sequences (the PBS-derived 40-nt-long DNA) or the PPT (61-nt-long DNA) These heteroduplexes were then elongated with the Klenow fragment of E. coli polymerase I (lacking the 3′→5′ exonuclease), thus producing full-length substrates.