Novel DNA sequence organization in rice genome

DNA sequence organization in rice genome has been investigated by studying the extent of DNA reassociation as a function of DNA fragment size. The reassociation kinetics curves indicate that there is no sequence interspersion of repeated and single-copy sequences at a DNA length of 6500 nucleotide pairs. The reassociation at lower $\text{C}{}_0\text{t}$ values, however, shows that there is an interspersion of DNA sequences within the repetitive DNA fraction. The size distribution of the repeated sequences is determined by agarose gel electrophoresis of $\text{C}{}_0\text{t}$ 50 DNA fraction of 6500-nucleotide-pair-long rice DNA digested with S₁ nuclease. About 35–40% of the S₁-resistant duplexes consist of 6000–6400 nucleotide pairs and 60–65% have a fragment size less than 150 nucleotide pairs. Among plants, rice is the first genome in which no DNA sequence interspersion is observed.