covalently closed circular DNA

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[Abbr. of deoxyribonucleic acid]
A complex nucleic acid of high molecular weight consisting of nucleotides made of deoxyribose, phosphoric acid, and one of four bases (two purines, adenine [A] and guanine [G], and two pyrimidines, thymine [T] and cytosine [C]). The nucleotides are arranged in a double helix (two long spirals twisting around each other) joined by hydrogen bonds between the complementary base pairs A-T and C-G. Nucleic acid, present in chromosomes of the nuclei of cells, is the chemical basis of heredity and the carrier of genetic information for all organisms except the RNA viruses. See: chromosome; gene; RNA; virus

complementary DNA

A double-stranded copy of a single-stranded RNA molecule, made by reverse transcriptase, an enzyme used by retroviruses such as HIV-1.

covalently closed circular DNA

Abbreviation: cccDNA
See: cccDNA

fecal DNA

Traces of nucleic acids found in the stool of people with colorectal cancers and polyps. Detection of DNA in stool has been proposed as an alternative to testing samples of stool for occult blood loss. Testing stool for traces of malignant DNA is a more sensitive screening test for intestinal cancer than screening stool samples for occult blood, but the test is expensive and is not as accurate a screening tool as colonoscopy.
Synonym: stool DNA testing

mitochondrial DNA

Abbreviation: mtDNA
DNA found in mitochondria. It differs from nuclear DNA in its nucleotide sequences, its size (about 16.5 kb), and its source (it is derived solely from the egg, not the sperm). Variations in mtDNA point to the ways in which members of a related population differ from each other genetically.

naked DNA

DNA that has been modified to remove the proteins that normally surround it. It is used for genetic transfers and vaccine manufacture.

recombinant DNA

Segments of DNA from one organism artificially manipulated or inserted into the DNA of another organism through gene splicing. When the host's genetic material is reproduced, the transplanted genetic material is also copied. Gene splicing permits isolation and examination of the properties and action of specific genes. See: plasmid; gene splicing

spacer DNA

Spacer sequence. See: Structure of DNA
Medical Dictionary, © 2009 Farlex and Partners

covalently closed circular DNA (CCC-DNA)

completely double-stranded circular DNA with no breaks or NICKS. It often adopts a supercoiled conformation, (see SUPERCOILED DNA). Compare OPEN CIRCULAR DNA.
Collins Dictionary of Biology, 3rd ed. © W. G. Hale, V. A. Saunders, J. P. Margham 2005
References in periodicals archive ?
(rc-DNA = relaxed circular DNA; HBV = hepatitis B virus; cccDNA = covalently closed circular DNA; pgRNA = pre-genomic RNA.)
(HBV = hepatitis B virus; rcDNA = relaxed circular DNA; HBsAg = hepatitis B surface antigen; cccDNA = covalently closed circular DNA; pgRNA = pre-genomic RNA.)
(V.) panamensis is an active endonuclease able to degrade covalently closed circular DNA, demonstrating that these regions are not critical to the functioning of this enzyme.
However, the challenge of antiviral therapy is to clear the HBV covalently closed circular DNA (cccDNA) pool.
In the mid-1970s, interferon-alpha began to be used to treat chronic hepatitis B (CHB), but the response rate to interferon-alpha treatment was low.[sup][2] After 1998, five nucleos(t)ide analogs (NAs)-lamivudine (LAM), adefovir dipivoxil (ADV), telbivudine (LdT), entecavir (ETV), and tenofovir disoproxil fumarate (TDF) were successively introduced, leading to a continuous virologic suppression and control of disease progression in CHB patients.[sup][3] NAs can inhibit viral replication by suppressing the process of reverse transcription, but they have a small effect in reducing intrahepatic covalently closed circular DNA (cccDNA).[sup][4] Therefore, long-term treatment might be beneficial to achieve the ultimate goal of clearance of hepatitis B surface antigen (HBsAg).[sup][5]
One-year entecavir or lamivudine therapy results in reduction of hepatitis B virus intrahepatic covalently closed circular DNA levels.