# How an Enzyme Helps Find Specific DNA in a Sample

> This patent describes a method for detecting a specific DNA sequence in a sample by using a labeled DNA probe and an enzyme that cuts the probe, releasing detectable fragments.

- **Patent:** US 5210015
- **Original title:** Homogeneous assay system using the nuclease activity of a nucleic acid polymerase
- **Owner:** Hoffmann La Roche Inc
- **Granted:** 1993
- **Status:** Public domain (expired)
- **Times cited:** 1,183
- **Field:** biotech, pharmaceutical, diagnostics, medical_devices, life_sciences

## What it does

This patent describes a process for finding a specific target nucleic acid (like DNA) in a sample. First, the sample is mixed with two short DNA pieces, called oligonucleotides. One oligonucleotide binds to a specific part of the target DNA, and a second, labeled oligonucleotide binds to another nearby part of the same target DNA strand (Claim 1a). Then, an enzyme called a template-dependent nucleic acid polymerase, which has a special ability to cut DNA from its 5' end (5' to 3' nuclease activity), is added (Claim 1b). This enzyme cuts the labeled oligonucleotide, releasing its detectable fragments. Finally, these released labeled fragments are detected and/or measured (Claim 1c). For example, this process can be used to detect a specific viral DNA sequence in a patient sample.

## What it does NOT cover

- Does not cover detection methods that do not use a labeled oligonucleotide.
- Does not cover systems where the nucleic acid polymerase lacks 5' to 3' nuclease activity.
- Does not cover methods where the first oligonucleotide's 3' end is not upstream of the labeled oligonucleotide's 5' end.
- Does not cover detection without the release of labeled fragments.
- Does not cover methods using only a single oligonucleotide probe for detection.
- Does not cover detection methods that rely solely on nucleic acid polymerization without nuclease activity.

## The clever bit

The truly novel aspect was using the nucleic acid polymerase's natural 5' to 3' nuclease activity to cleave a labeled probe *during* the DNA synthesis process itself. This allowed for simultaneous amplification and detection, eliminating the need for separate post-amplification detection steps.

## Real-world examples

1. TaqMan assays for gene expression analysis
2. Quantitative PCR (qPCR) diagnostics
3. COVID-19 diagnostic tests
4. Detection of pathogens in food safety
5. Genetic screening for inherited diseases

## Why it matters

This patent laid the groundwork for a widely used molecular diagnostic technique known as TaqMan, or probe-based real-time PCR. It provided a way to detect and quantify specific DNA or RNA sequences in real-time during a PCR amplification. This innovation significantly sped up and simplified genetic testing, making it a cornerstone for research, medical diagnostics, and forensic science.

## Frequently asked questions

### What does How an Enzyme Helps Find Specific DNA in a Sample cover?

This patent describes a method for detecting a specific DNA sequence in a sample by using a labeled DNA probe and an enzyme that cuts the probe, releasing detectable fragments.

### Who owns patent US 5210015?

Hoffmann La Roche Inc owns this patent, granted in 1993.

### When does this patent expire?

This patent has expired and is now in the public domain — anyone can use the invention freely.

### What is patent US 5210015 cited by?

This patent has been cited by 1183 later patents that build on its ideas.

### What problem does this patent solve?

This patent laid the groundwork for a widely used molecular diagnostic technique known as TaqMan, or probe-based real-time PCR. It provided a way to detect and quantify specific DNA or RNA sequences in real-time during a PCR amplification. This innovation significantly sped up and simplified genetic testing, making it a cornerstone for research, medical diagnostics, and forensic science.

### What does this patent NOT cover?

Does not cover detection methods that do not use a labeled oligonucleotide.

**Full plain-English explainer:** https://patentbrief.org/patent/us/5210015/hcv-pcr-detection

**Original patent:** https://patents.google.com/patent/US5210015

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_Source: PatentBrief — https://patentbrief.org. Patent facts are from public records; the plain-English explanation is PatentBrief's._