Practice question

Accurate mapping of transcription start sites is essential for promoter analysis. Cap Analysis of Gene Expression specifically captures the 7-methylguanosine cap structure present at 5 prime ends of eukaryotic messenger RNAs. After reverse transcription, cap-trapped complementary DNAs are cleaved and 20-27 base tags adjacent to cap are isolated and sequenced, directly identifying start sites at single nucleotide resolution. RNA-seq maps entire transcripts but lacks focused resolution for initiation sites. Northern blot and SAGE measure size and abundance but cannot precisely define transcription start sites genome-wide, making CAGE superior.