DNA attachment to the hamster sperm nuclear matrix and nuclear annulus.

Hamster sperm DNA is packaged so tightly that it is the most highly condensed eukaryotic DNA known. Nevertheless, the sperm genome is also organized in a very specific fashion by two nuclear structures, the nuclear matrix and the nuclear annulus. The nuclear matrix organizes sperm DNA into loop domains approximately 46 Kb in length by specific attachment sequences. When the sperm nucleus is induced to decondense, the nuclear matrix almost completely dissipates, leaving only the nuclear annulus, a structure located at the implantation fossa within the nucleus. All the DNA remains anchored to the annulus during decondensation. Rotary shadowing transmission electron microscopy of isolated nuclear annuli retaining only a small portion of this anchored DNA suggests that the DNA is anchored to the annulus in a series of mini-loops, 5-10 Kb in length. These data support our previous suggestions that sperm DNA is organized in a very specific manner.