Analysis of the low molecular weight nuclear polypeptide by isoelectrofocusing of nuclear proteins first separated by gel electrophoresis in SDS.

Some of the nuclear proteins, especially those tightly bound with nucleic acids, show a tendency to aggregate and some of them are also hydrophobic. Thus, SDS-containing buffers are useful for their analysis. The method of isoelectrofocusing of proteins separated by polyacrylamide gel electrophoresis in the presence of SDS was used for the analysis of the nuclear proteins. First, SDS-polyacrylamide gel electrophoresis of total chromatin proteins was conducted. The sample of the examined nuclear proteins after SDS-gel electrophoresis was isolated as a gel slice (thus corresponding to the particular molecular weight range) and used for isoelectrofocusing. This approach has been used for the analysis of about 19 kD nuclear polypeptide, tightly bound with DNA. The isoelectric point of this polypeptide has been estimated as 5.3.