Patent ID: 6773887
Filing Date: 2004-08-10
Classification: C12Q

Abstract:
A method for determining the number of repeat units in a repeat region of a target nucleic acid, said method comprising the steps of:(a) annealing a primer-complementary portion of a target nucleic acid to a primer thereby forming a target-primer hybrid; (b) performing a first primer extension reaction using a first primer extension reagent, wherein the first primer extension reagent allows said first primer extension reaction to proceed only to the extent that said primer is extended by an amount less than a full repeat unit; (c) separating the target-primer hybrid and unreacted first primer extension reagent; (d) performing a second primer extension reaction using a second primer extension reagent, wherein the second primer extension reagent allows said second primer extension reaction to proceed only to the extent that the portion of said full repeat unit not synthesized by the first primer extension reagent is synthesized and wherein at least one of the first or second primer extension reagents includes an extendible nucleotide having a label attached thereto; (e) separating the target-primer hybrid from unreacted second primer extension reagent; (f) measuring a signal produced by the label; (g) treating the label so as to render the label undetectable; (h) repeating a cycle of steps (a) through (g) until the signal is substantially less than a signal detected in a previous cycle; and (i) determining the number of repeat units in said repeat region of said target nucleic acid.