Identification of the cystic fibrosis gene: chromosome walking and jumping

Article Abstract:

Cystic fibrosis is characterized by abnormally thick mucous secretions, particularly in the lungs; the disease leads to infection and death at an early age. One in every 2,000 children is born with this fatal disease. The genetic code for the protein involved in cystic fibrosis has been identified, using the molecular biological techniques known as chromosome walking and jumping. The cystic fibrosis gene is located on the seventh chromosome. Chromosomes are structures composed of DNA, deoxyribonucleic acid, which contains the information for producing the molecules involved in the processes of life. Using other genes, known as marker genes, which are also located on chromosome seven, the exact location of the cystic fibrosis gene was pinpointed. The molecular sequences of the nucleic acids that compose the DNA surrounding the known genes were identified. This was done using overlapping clones of DNA, stretches of DNA that contained sequences that are known and other sequences that are not known. The unknown DNA was then sequenced and used to isolate other clones containing additional DNA whose sequence was not known. Using this method, known as "walking the chromosome", the entire region surrounding the marker genes was sequenced and analyzed for a gene that could code for a molecule involved in cystic fibrosis. However, because there was a very large amount of DNA between the known genes, walking the chromosome would have taken a long time and would have been a tremendous amount of work with many technical problems. Instead, the investigators used a technique called "jumping the chromosome", where they passed by large amounts of DNA that clearly did not contain the sequence they were looking for. The reason the gene for cystic fibrosis was so difficult to isolate was because the gene was not deleted or rearranged as are so many genes in the disease state. The techniques, walking and jumping the chromosome, can be used to isolate other genes involved in diseases that are also difficult to isolate.

Methods, Chromosomes

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Identification of the cystic fibrosis gene: cloning and characterization of complementary DNA

Article Abstract:

Cystic fibrosis is a disease which is characterized by abnormally thick mucous secretions, particularly in the lungs; the condition leads to infection and death at an early age. One in every 2,000 children is born with this fatal disease. The genetic code for the protein involved in cystic fibrosis has been identified. DNA clones, sequences of deoxyribonucleic acid, were isolated and analyzed for the cystic fibrosis gene. By comparing the gene found in normal individuals with the gene found in individuals with cystic fibrosis, it was discovered that one amino acid (the building blocks of protein molecules) was missing in individuals with cystic fibrosis. The gene for cystic fibrosis codes for a protein that is similar to other proteins. These other proteins are found on the cell membrane and are involved in the transport of ions, small electrically charged molecules, across the membrane. Other data show that cells isolated from patients with cystic fibrosis do not transport chloride ions across their membranes as well as cells from unaffected individuals, which could lead to abnormally thick mucous. Additional research is necessary to understand how the deletion of one amino acid could affect the protein to bring about symptoms of the disease. This understanding could lead to the development of treatments and possibly a cure for cystic fibrosis.

Ion channels

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Identification of the cystic fibrosis gene: genetic analysis

Article Abstract:

Cystic fibrosis is characterized by abnormally thick mucous secretions, particularly in the lungs; the condition leads to infection and death at an early age. One in every 2,000 children is born with this fatal disease. The genetic code for the protein involved in cystic fibrosis has been identified. Approximately 70 percent of 214 cystic fibrosis patients studied have a deletion of one amino acid, the building blocks of proteins, in the protein coded for by the cystic fibrosis gene. This mutation was not present in 198 individuals who did not have the disease, suggesting that this mutation is in fact the cause of the disease. The other 30 percent of the patients with cystic fibrosis had various changes in the DNA. The molecular defects of these changes are not yet understood. Knowing the defects in the DNA, deoxyribonucleic acid, the molecular sequence that comprises genes, will make prenatal and natal diagnosis of cystic fibrosis easier and more accurate.

Chromosome mapping, Prenatal diagnosis

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