Amino acid and protein metabolism during differentiation (sclerotization) of the myxomycete Physarum flavicomum

Differential synthesis of histone H1 during early spherulation in Physarum polycephalum

H1 and P2 (an H1 degree/HMG-like protein) accumulate during exponential growth of Physarum microplasmodia (unpublished results), indicating that these proteins may play a role in differentiation (spherulation). To test this hypothesis, pulse labelling using [14C]lysine was used to determine whether any differential histone synthesis occurs during salts-induced spherulation. A peak in the uptake of [14C]lysine into microplasmodia was detected between 12 and 24 h following salts-induction. During the same interval, incorporation of label into the CaCl2-extracted histones occurred, with H1 being synthesised at approx. 3 times the level of the core histones and P2. Densitometry of SDS-PAGE gels showed that high levels of H1 were maintained up to 40 h in salts medium, beyond the observed peak in synthesis. The synthesis and accumulation of high levels of H1 during early spherulation indicates a role for this histone in the initiation and maintenance of a transcriptionally inactive differentiated state.

Multiple acid proteinases in the cellular slime mould Dictyostelium discoideum

Proteinase activity in the cellular slime mould Dictyostelium discoideum has been analyzed by electrophoresis on polyacrylamide gels containing denatured hemoglobin. At least eight bands due to acid proteinases have been defined using extracts of myxamoebae, four bands A-D which move faster than the fifth and major band E, a minor band E' which moves just behind E and two slow bands G and H. Fruiting body formation was accompanied by the appearance of one new proteinase band F. The proteinases were present in extracts of both axenically-grown and bacterially-grown cells. Differences between the pH dependence and stability of the individual proteinases were detected. Inhibitor studies suggested that the faster proteinases A-D may be cathepsin B-like, whilst the slower enzymes E, E' and F do not fit readily into any known group of proteinases since they were sensitive to HgCl2 but not to other inhibitors of cathepsin B and not to inhibitors of cathepsin D-like proteinases under standard conditions. None of the proteinases was apparently formed during or after preparation of extracts and the proteinases could be re-run on polyacrylamide gels to give only the band expected from the first run. The bands are believed to reflect multiple proteinase activities within the cell.