Browsing by Author "Pahlic, Mira"

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    Changes in proteins during the cell cycle of Physarum polycephalum
    Pahlic, Mira (Virginia Polytechnic Institute and State University, 1982)
    To determine how many changes in proteins occur during the cell cycle of a primitive eukaryote Physarum polycephalum, total plasmodial proteins were resolved by two-dimensional gel electrophoresis and visualized by a sensitive silver stain. The results indicate that most proteins do not change in concentration during the cell cycle. The one protein which changed consistently on the gels had a 32,000 molecular weight and isoelectric point of 4.9. This protein increased in concentration during early prophase, peaked in metaphase and decreased by a factor of five by one hour after metaphase. The identity of this protein is not known. Four forms of actin were purified and identified on two-dimensional gels. Their molecular weight was 43,000 with three isoelectric points near 4.7 and one at 5.1. All four forms bound to DNase I agarose. The amino acid composition of Physarum actin was very similar to that of rabbit actin, also containing a characteristic modified amino acid, 3-methyl histidine. All four forms were also identified in gels of nuclear proteins. Five species of thymidine kinase were identified on isoelectric focusing gels from their characteristic activities. TIP inhibited all five forms. The isoelectric points of these forms were 5.9, 6.4, 6.7, 6.9 and 7. 1. The four most acidic forms first appear about one hour before metaphase, peak in telophase and decline during S phase. The 5.9 form is the first to decrease in activity followed by the 6.4 and 6. 7 forms. The activity of the 7.1 form did not change significantly during the entire cell cycle.