DEOXYRIBONUCLEIC-ACID SEQUENCE ORGANIZATION IN THE MUNG BEAN GENOME

Deoxyribonucleic acid (DNA) reassociation kinetics were used to characterize repeated and single-copy sequences in the mung bean (Vigna radiata) genome and to analyze the interspersion of single-copy and repeated sequences. Experiments with 300 nucleotide long fragments of total DNA as well as with a purified single-copy fraction show that the most slowly reassociating sequences do so with a rate of 1.6ËŸ10-3 when assayed with hydroxylapatite. This rate is~105 times slower than that observed for Escherichia coli DNA included as an internal standard, and thus the kinetic complexity of the mung bean genome is ~4.7ËŸ108 nucleotide pairs or 0.48 pg/haploid nucleus. This value is in good agreement with cytophotometric measurements and makes the mung bean genome the smallest yet characterized among higher plants. About 35% of the total root DNA fragments contain repetitive sequences. However, total leaf DNA preparations contain an additional 11% rapidly renaturing fraction, which is attributable to chloroplast DNA. The reassociation kinetics of repetitive DNA can be modeled with a single the oretical second-order component, but the data do not specify a unique solution. The reassociation kinetics of isolated high-and low-frequency fractions indicate that repetitive sequence families probably cover a range from about fifty to several thousand copies per haploid genome. Long tracer reassociation kinetics at three different fragment lengths indicate that ~35% of the single-copy sequences are interspersed with repetitive sequences at distances between 300 and 1200 nucleotide pairs, and an additional 18% of the single-copy sequences are interspersed between 1200 and 6700 nucleotide pairs. About 46% of the single-copy sequences are not interspersed with repeats at a distance of 6700 nucleotide pairs. While the distances at which the latter sequences might be interspersed are unknown, it appears that sequence organization in the mung bean covers the entire spectrum from short- to long-period interspersion. The pattern of sequence repetition and arrangement in mung bean DNA differs dramatically from that previously observed in the garden pea, which is a member of the same subfamily. © 1979, American Chemical Society. All rights reserved.