Isolation of a residual protein structure from nuclei of the myxomycete Physarum polycephalum.

A nuclear framework structure has been obtained from isolated interphase nuclei of Physarum polycephalum by extraction with 2.5 M NaCl and subsequent digestion with DNase. Whole-mount electron micrographs showed a nuclear lamina containing residual pore structures associated with the fibrous internal matrix. The matrix was continuous with fibrillar remnants of the nucleolus. The structure was shown to consist of 2 major polypeptides of 23,000 and 36,500 Daltons as well as 30 to 40 minor polypeptides of various molecular weight classes. The 2 major polypeptides were also prominent in preparations of the residual nucleolar material, suggesting that matrix proteins are common to both structures. The predominance of low-molecular-weight polypeptides in Physarum nuclear matrix suggests that there may be significant differences in composition of nuclear structural proteins between lower and higher eukaryotes.