Characterization of the genome of Phycomyces blakesleeanus.

DNA of Phycomyces blakesleeanus was extracted from whole mycelia and from nuclear and mitochondrial organelle fractions obtained from sporangiophores. DNA from all three sources exhibits one symmetrical band at p equals 1.688 g/ml in CsCl buoyant density gradients. Reassociation data are consistent with kinetic division of the DNA into three components: very rapidly renaturing (fraction I), rapidly reassociating (fraction II) and slowly reassociating (fraction III) base sequences. These components comprise approximately 10%, 20% and 64% of total cell DNA. Kinetic fractions were prepared from total cell DNA and reassociated separately. The corrected rate constant is 11.3 M-1-S-1 for the rapidly reassociating component and 0.055 M-1-S-1 for the slowly reassociating component. Based on these data and the data from unfractionated total cell DNA, the genome size of Phycomyces is approximately 1.9-10-10 daltons, 6.7 times that of Escherichia coli.