Interdigitated repeated sequences in bovine satellite DNA

Abstract

MOST eukayrote genomes contain some highly repeated DNA sequences. DNA hybridisation kinetic studies indicate that the smallest repeating unit of highly repetitious DNA is around 300 base pairs¹ but direct sequence analysis of highly repeated DNA has demonstrated a simple basic repeating unit of 4–12 nucleotides^2–5. It has been postulated that the repeated sequences have been generated by successive replications of some primary simple sequence^{1, 6, 7}. The discrepancy between sequence data and kinetic analysis may be explained by noting that the rate of reassociation is a function of length⁸; this data is consistent with a model of internal heterogeneity in the repeated, simple DNA sequence units^{9, 10}. Although the hybridisation and sequence analyses have been successful in establishing certain features of reiteirated DNA, these methods are not well suited to detect and study infrequent but regularly repeated DNA sequences interdigitated within the dominant short repeating units. The existence and nature of such interdigitated repeats are important to our understanding of the mechanism by which repeated DNA is generated. We have used site-specific endonucleases (restriction enzymes) to show that mutational events within simple sequence DNA may have been coupled with cycles of discrete replications.