The Primer Extension System is used to determine the location and level of a target 5´-end of RNA. The system uses AMV Reverse Transcriptase (Cat.# M5101, M5108 and M9004) and an end-labeled primer to reverse transcribe the target RNA into cDNA. The amount of cDNA synthesized is proportional to the amount of target RNA, and the length of the cDNA product reflects the distance from the primer to the 5´-end of the RNA. Primer extension products are typically analyzed on denaturing polyacrylamide gels, and the use of labeled DNA markers allow the size of the primer extension product to be determined. The Kanamycin Positive Control RNA (Cat.# C1381), provided in the form of a 1.2kb in vitro transcription product, has a primer extension product that is 87 bases in length.