Characterization of Allomyces genome.

Allomyces arbuscula DNA isolated from whole cells (bulk DNA) is composed of a major (alpha) and two minor components (beta & gamma) with buoyant densities in neutral CsCl corresponding to 1.721, 1.710 and 1.702 g/cm3, respectively. The DNA obtained from purified nuclei contains alpha component only. The beta component corresponds to mitochondrial DNA. The gamma component is also extra-nuclear but has not been characterized. The reassociation kinetics of sheared, bulk and nuclear DNA show that (i) 25 % bulk and 10% of nuclear DNA reanneal very rapidly and contain highly repeated sequences; (ii) moderately repeated sequences, accounting for 15% of both bulk and nuclear DNA, have a sequence complexity of approximately 7.2-10(6) daltons and are repeated about 320 times; (iii) the slow reannealing fraction accounts for about 60% of the genome and has kinetic properties similar to single copy sequences. The sequence complexity of this fraction was determined in relation to that of Escherichia coli. After a correction for the size of the repeated sequences the genome size of A. arbuscula was calculated to be 1.7-10(10) daltons.