Primer extension.

Primer extension can be viewed as a technique complementary to S1 nuclease mapping (see Chapter 43). In Sl nuclease mapping analysis, a DNA:RNA hybrid is resected back to the point of divergence between the RNA and the DNA. In primer extension, a DNA probe is annealed to an RNA template and then extended in a 3';- 5'; direction to the start of the RNA molecule. The most common usages for this technique are in determining the size of full-length RNA transcripts and mapping transcription initiation sites.