Practice question

5'-end labeling introduces a label specifically at the 5' terminus of DNA. T4 polynucleotide kinase catalyzes transfer of the gamma-phosphate from ATP to a free 5'-hydroxyl group of DNA or RNA. When [gamma-32P]ATP is supplied as substrate, a radioactive phosphate is efficiently added to the 5' end, creating a highly detectable probe. Prior dephosphorylation with alkaline phosphatase increases labeling efficiency. This technique labels restriction fragments and synthetic oligonucleotides for sequencing, primer extension, and electrophoretic mobility shift assays, whereas polymerases and ligases perform distinct functions.