Daniel G. Peterson ^{1, 4}, Stefan R. Schulze ^{1, 3}, Erica B. Sciara ^{1, 3}, Scott A. Lee ¹, John E. Bowers ¹, Alexander Nagel ², Ning Jiang ², Deanne C. Tibbitts ¹, Susan R. Wessler ², and Andrew H. Paterson ^{1, 2}

¹ Center for Applied Genetic Technologies and Department of Crop and Soil Sciences, University of Georgia, Athens, Georgia 30602, USA;
² Department of Botany and Department of Genetics, University of Georgia, Athens, Georgia 30602, USA

³ These authors contributed equally to the research. They are listed in alphabetical order.
⁴ Corresponding author. Plant Genome Mapping Laboratory, University of Georgia, Room 162, Riverbend Research Bldg., 110 Riverbend Road, Athens, GA 30602, USA
E-mail:   dgp@arches.uga.edu

Cot-based sequence discovery represents a powerful means by which both low-copy and repetitive sequences can be selectively and efficiently fractionated, cloned, and characterized. Based upon the results of a Cot analysis, hydroxyapatite chromatography was used to fractionate sorghum (Sorghum bicolor) genomic DNA into highly repetitive (HR), moderately repetitive (MR), and single/low-copy (SL) sequence components that were consequently cloned to produce HRCot, MRCot, and SLCot genomic libraries. Filter hybridization (blotting) and sequence analysis both show that the HRCot library is enriched in sequences traditionally found in high-copy number (e.g., retroelements, rDNA, centromeric repeats), the SLCot library is enriched in low-copy sequences (e.g., genes and "nonrepetitive ESTs"), and the MRCot library contains sequences of moderate redundancy. The Cot analysis suggests that the sorghum genome is approximately 700 Mb (in agreement with previous estimates) and that HR, MR, and SL components comprise 15%, 41%, and 24% of sorghum DNA, respectively. Unlike previously described techniques to sequence the low-copy components of genomes, sequencing of Cot components is independent of expression and methylation patterns that vary
widely among DNA elements, developmental stages, and taxa. High-throughput sequencing of Cot clones may be a means of "capturing" the sequence complexity of eukaryotic genomes at unprecedented efficiency.

[Online supplementary material is available at www.genome.org The sequence data described in this paper have been submitted to the GenBank under accession nos. AZ921847-AZ923007. Reagents, samples, and unpublished information freely provided by H. Ma and J. Messing.] 

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6. Frenster JH, "Ultrastructural Probes of Active DNA Sites, and the RNA Activators of DNA".

7. Frenster JH, "Activation of DNA Transcription within Repressed Chromatin".

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