Practice question

Labeling cohesive ends commonly employs DNA polymerases that can fill in 5' overhangs. T4 DNA polymerase possesses strong 3' to 5' exonuclease and polymerase activity that efficiently incorporates labeled dNTPs opposite the single-stranded overhang using the protruding 5' sequence as template. EcoRI is restriction enzyme that creates ends, not label them. Ligase joins fragments, exonuclease III degrades from 3' terminus. Hence T4 polymerase is standard choice for labeling sticky ends in mapping, footprinting, and terminal labeling protocols using radioactive or fluorescent nucleotides.