Synthesis of protein during the nuclear division cycle in Physarum polycephalum

Regulation of Protein Synthesis in the Plasmodial Phase of Physarum polycephalum

“…Thereafter it increases until by late G2 phase it has doubled by comparison with the rate in S phase. These findings agree with previous work [5], in which the protein accumulation curvc was derived by combining the nucleic acid/protein ratio and the synthesis of total nucleic acid, determined by isotope dilution after labelling with [3H]uridine.…”

“…The synthesis of protein between successive nuclear divisions has previously been determined by pulse-labelling with ["S]-methionine [4] and by an indirect reference to the synthesis of total nucleic acid [5]. However, unequivocal interpretation of pulse-labelling experiments is difficult, and the number of measurements required in the other study led to considerable experimental error in the values calculated for the increment in protein.…”

“…The remainder of the cycle (6 -7 h) is occupied by G2 phase; mitosis itself only lasts 20-30 min.The natural synchrony characteristic of the plasmodial phase of Physarum makes it a useful organism for the study of biochemical processcs in relation to nuclear division. The synthesis of protein between successive nuclear divisions has previously been determined by pulse-labelling with ["S]methionine [4] and by an indirect reference to the synthesis of total nucleic acid [5]. However, unequivocal interpretation of pulse-labelling experiments is difficult, and the number of measurements required in the other study led to considerable experimental error in the values calculated for the increment in protein.…”

“…However, unequivocal interpretation of pulse-labelling experiments is difficult, and the number of measurements required in the other study led to considerable experimental error in the values calculated for the increment in protein. Initially it was considered [5] that the isotope dilution method, developed for the study of metabolically stable nucleic acids [3], would not be directly applicable to the analysis of protein synthesis, because of the largely unknown extent of protein turnover. Further reflection suggested that amino acid labelling could be used provided that sufficient growth in tinlabelled medium was allowed before beginning specific activity measurements.…”

Oxygen Uptake and Mitochondrial Enzyme Activities in the Mitotic Cycle of Physarum polycephalum

“…It may therefore be significant that Fink (1975) has reported fluctuations in the UTP pool in synchronously growing P. polycephalum which might account for the pattern of uridine incorporation observed by Mittermayer et al (1964). Evidence obtained by other techniques indicates that, apart from a brief stoppage during mitosis itself, the rate of synthesis of RNA (Nygaard et al, 1960;Hall & Turnock, 1976) and of protein (Mittermayer et al, 1966;Brewer, 1972;Birch & Turnock, 1977) increases continuously between one mitosis and the next. An alternative explanation may therefore have to be found for the pattern of respiration in P .…”