Trout sperm chromatin. II. Ultrastructural aspects after salt dissociation of proteins.

The ultrastructural organization of the trout sperm nucleus was studied in ultrathin sections and spread preparations after partial decondensation of the nucleus with increasing NaCl concentrations. The obtained results suggest that the organization of the trout sperm chromatin is much more complex than a pure nucleoprotamine. Three types of complexes were observed. The first one results from the association of DNA with protamines. This complex appears as a fibrous network when partially decondensed nuclei are digested with DNase I indicating that at least a part of DNA remains protected by protamines and favours models accepting a colinear alignment of the latter on the DNA molecules. The second type of structures represent the DNA-protamine fibers compacted into dense clumps which appear as separate compaction units seen upon partial decondensation of the sperm nucleus. A third type are complexes of the ring-shaped granular bodies tightly associated with DNA and resisting high salt-urea and detergent treatment.