Practice question

Determination of the authentic 5 prime end of a transcript requires extension of a labeled primer annealed downstream. In primer extension, reverse transcriptase synthesizes complementary DNA until reaching the extreme 5 prime terminus of messenger RNA, generating product whose length indicates transcriptional start site. Northern blotting estimates size and abundance but lacks nucleotide resolution at ends. S1 mapping provides approximate termini, while 3 prime RACE specifically targets the polyadenylated tail. Therefore, primer extension remains a classical method of choice for high-resolution mapping of 5 prime ends.