L. S. Cram

Bio: L. S. Cram is an academic researcher from Los Alamos National Laboratory. The author has contributed to research in topics: Repeated sequence & Chromosome. The author has an hindex of 5, co-authored 5 publications receiving 2622 citations.

A highly conserved repetitive DNA sequence, (TTAGGG)n, present at the telomeres of human chromosomes.

Abstract: A highly conserved repetitive DNA sequence, (TTAGGG)n, has been isolated from a human recombinant repetitive DNA library. Quantitative hybridization to chromosomes sorted by flow cytometry indicates that comparable amounts of this sequence are present on each human chromosome. Both fluorescent in situ hybridization and BAL-31 nuclease digestion experiments reveal major clusters of this sequence at the telomeres of all human chromosomes. The evolutionary conservation of this DNA sequence, its terminal chromosomal location in a variety of higher eukaryotes (regardless of chromosome number or chromosome length), and its similarity to functional telomeres isolated from lower eukaryotes suggest that this sequence is a functional human telomere.

Human chromosome-specific repetitive DNA sequences: novel markers for genetic analysis

Abstract: Two recombinant DNA clones that are localized to single human chromosomes were isolated from a human repetitive DNA library. Clone pHuR 98, a variant satellite 3 sequence, specifically hybridizes to chromosome position 9qh. Clone pHuR 195, a variant satellite 2 sequence, specifically hybridizes to chromosome position 16qh. These locations were determined by fluorescent in situ hybridization to metaphase chromosomes, and confirmed by DNA hybridizations to human chromosomes sorted by flow cytometry. Pulsed field gel electrophoresis analysis indicated that both sequences exist in the genome as large DNA blocks. In situ hybridization to intact interphase nuclei showed a well-defined, localized organization for both DNA sequences. The ability to tag specific human autosomal chromosomes, both at metaphase and in interphase nuclei, allows novel molecular cytogenetic analyses in numerous basic research and clinical studies.

Human chromosome–specific DNA libraries: Construction and availability

Abstract: The goal of the National Laboratory Gene Library Project at the Los Alamos and Lawrence Livermore National Laboratories is the production of chromosome–specific human gene libraries and their distribution to the scientific community for studies of the molecular biology of genes and chromosomes, and for the study and diagnosis of genetic disease. The specific aim of Phase I of the project is the production of complete digest (4 kb average insert size) libraries from each of the 24 human chromosomal types purified by flow sorting. The bacteriophage vector is Charon 21A, which has both Eco R1 and Hind III insertion sites accommodating human DNA fragments up to 9.1 kb in size. Each laboratory has undertaken production of a complete set of chromosome–specific libraries, Los Alamos with Eco R1 and Livermore with Hind III; most of this task has now been accomplished. Close to 1200 library aliquots have been sent to about 300 laboratories world–wide through February 1986, at which time repository and distribution functions were transferred to the American Type Culture Collection, Rockville, Md. Following Phase I, we will begin the construction of libraries with large inserts in a more ad vanced, recently developed bacteriophage vector (about 20 kb inserts) or in a cosmid vector (about 40 kb inserts), and with characteristics better suited to basic studies of gene structure and function.

Specific association of human telomerase activity with immortal cells and cancer

Abstract: Synthesis of DNA at chromosome ends by telomerase may be necessary for indefinite proliferation of human cells. A highly sensitive assay for measuring telomerase activity was developed. In cultured cells representing 18 different human tissues, 98 of 100 immortal and none of 22 mortal populations were positive for telomerase. Similarly, 90 of 101 biopsies representing 12 human tumor types and none of 50 normal somatic tissues were positive. Normal ovaries and testes were positive, but benign tumors such as fibroids were negative. Thus, telomerase appears to be stringently repressed in normal human somatic tissues but reactivated in cancer, where immortal cells are likely required to maintain tumor growth.

Structure and function of telomeres

Abstract: The DNA of telomeres--the terminal DNA-protein complexes of chromosomes--differs notably from other DNA sequences in both structure and function. Recent work has highlighted its remarkable mode of synthesis by the ribonucleoprotein reverse transcriptase, telomerase, as well as its ability to form unusual structures in vitro. Moreover, telomere synthesis by telomerase has been shown to be essential for telomere maintenance and long-term viability.

Multiplexed electrical detection of cancer markers with nanowire sensor arrays.

Abstract: We describe highly sensitive, label-free, multiplexed electrical detection of cancer markers using silicon-nanowire field-effect devices in which distinct nanowires and surface receptors are incorporated into arrays. Protein markers were routinely detected at femtomolar concentrations with high selectivity, and simultaneous incorporation of control nanowires enabled discrimination against false positives. Nanowire arrays allowed highly selective and sensitive multiplexed detection of prostate specific antigen (PSA), PSA-a1-antichymotrypsin, carcinoembryonic antigen and mucin-1, including detection to at least 0.9 pg/ml in undiluted serum samples. In addition, nucleic acid receptors enabled real-time assays of the binding, activity and small-molecule inhibition of telomerase using unamplified extracts from as few as ten tumor cells. The capability for multiplexed real-time monitoring of protein markers and telomerase activity with high sensitivity and selectivity in clinically relevant samples opens up substantial possibilities for diagnosis and treatment of cancer and other complex diseases.

A highly conserved repetitive DNA sequence, (TTAGGG)n, present at the telomeres of human chromosomes.

Abstract: A highly conserved repetitive DNA sequence, (TTAGGG)n, has been isolated from a human recombinant repetitive DNA library. Quantitative hybridization to chromosomes sorted by flow cytometry indicates that comparable amounts of this sequence are present on each human chromosome. Both fluorescent in situ hybridization and BAL-31 nuclease digestion experiments reveal major clusters of this sequence at the telomeres of all human chromosomes. The evolutionary conservation of this DNA sequence, its terminal chromosomal location in a variety of higher eukaryotes (regardless of chromosome number or chromosome length), and its similarity to functional telomeres isolated from lower eukaryotes suggest that this sequence is a functional human telomere.