Figure 1.

Assay design for repeat length determination in simple repeats and enhanced sequence analysis in interrupted and compound microsatellites. STR loci are amplified with promoter-tagged primers (step 1) and transcribed into RNA by viral RNA polymerases (step 2). A G-specific RNA cleavage reaction is performed (step 3) to extract the intact repetitive core sequence (containing no G) from the full-length transcript in simple STRs. The resulting fragments then are analysed according to the number of repeat units (step 4). However, cleavage of RNA transcripts from interrupted and compound STRs containing Gs in the repetitive core sequence, allows for further characterisation of mutational events by MALDI-TOF analysis of the cleavage products (step 4).