Chinese Hamster Nuclear Proteins

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Abstract
A comparison by 2-dimensional gel electrophoresis of total interphase nuclear, metaphase chromosomal and nuclear matrix proteins from Chinese hamster V-79 cells was undertaken to examine the distribution of these proteins during mitosis. A number of differences were found among these populations, although the 2-dimensional gel patterns are generally similar. The most striking observation is that a loose cluster of 6 interphase nuclear polypeptides, with isoelectric points in urea between 5.7-6.7 and molecular masses ranging from 53-75 kDa [kilodalton], is greatly enriched in chromosome preparations. Each of these species is also prominent in the nuclear matrix. Preliminary evidence suggests that 1 of these polypeptides is the intermediate filament protein, vimentin. In addition, 2 major polypeptides of interphase nuclear preparations, a basic 94 kDa species and an .apprx. 65 kDa species, are absent from chromosomes. The latter polypeptide is the nuclear pre-lamina complex lamin B. Actin is present in all of these fractions, but tubulin was not observed. hnRNP [heterogeneous nuclear ribonucleoprotein] particle polypeptides are major components of the nuclear matrix, but are markedly reduced in metaphase chromosomes. The intermediate and basic 65-75 kDa nuclear matrix polypeptides, previously demonstrated to be major components of rat liver nuclear matrix, are reduced in Chinese hamster matrix preparations; at least 1 of these species, a minor, basic 68 kDa polypeptide, is missing entirely from metaphase chromosomes. These results are discussed in relation to nuclear and chromosome structure and the possibility of contamination of nuclear protein preparations from cultured cell lines with intermediate filaments.