Physiological control of phosphorylation ribosomal protein S6 in Mucor racemosus

Abstract

Minimal media were prepared from 0.05% yeast nitrogen base (Difco) without a nitrogen or carbon source.Ammonium-glucose and ammonium-glycerol media were prepared from the yeast nitrogen base by adding 10 mM ammonium chloride and 2% glucose or glycerol. Glutamate-glucose and glutamate-glycerol media were prepared from yeast nitrogen base by adding 10 mM L-glutamate and 2% glucose or glycerol. The media were adjusted to pH 4.5 with sulfuric acid.

Stored mRNA in sporangiospores of the fungus Mucor racemosus

“…One intriguing possibility is that the adjustment of ribosome function observed here is controlled by a protein kinase. Protein S-6 of the 40S ribosomal subunit shows a degree of phosphorylation that directly correlates with the rates of cell growth and protein synthesis (9). The S-6 protein is unphosphorylated in dormant sporangiospores of M. racemosus but rapidly becomes phosphorylated during germination (8).…”

Mucor dimorphism.

“…A basic protein (designated S6) from the small ribosomal subunit displays various degrees of phosphorylation, which is a strong correlate of the level of protein synthetic activity in most eukaryotic organisms (122,124). The degree of S6 phosphorylation shows a direct correlation with cell morphology, rate of protein synthesis, and intracellular ATP concentration during C02-to-air-in-duced yeast-to-hypha conversions and sporangiospore germination in M. racemosus (119,120).…”

“…M. racemosus cells shifted from a nitrogen atmosphere to air convert from yeasts to hyphae; however, the instantaneous rate of protein synthesis, the percentage of ribosome recruitment into polysomes, and the rate of peptide bond formation show little increase over the relatively high levels normally found in yeasts grown under nitrogen (155,189,190). The degree of S6 phosphorylation was described as nutrition and growth rate dependent under circumstances in which no morpho-genesis takes place (120). It is possible that the mere absence of CO2 derepresses certain functions necessary for yeast-tohypha morphogenesis, some perhaps related to the rate of protein synthesis, but they alone are not sufficient to allow morphogenesis to go on in the absence of oxygen.…”

Changes in robosomal properties during adenylate deprivation in the cells of Kluyveromyces lactis

“…Changes in a r-protein, mammalian S6 or its equivalent in other organisms, have been reported extensively as being due to different degrees of the phosphorylation of the protein under various nutrient conditions (see Lastick et al, 1977;Kristiansen and Kruger, 1979, as examples). In a lower eukaryote, Mucor rencemosus, the level of r-protein phosphorylation was found closely correlated to change in intracellular ATP pool size (Larsen and Sypherd, 1980). Changes in r-protein patterns observed in the present study, however, may not be due to the direct effects of protein phosphorylation, since the changed patterns in 2-D gels differed from those anticipated in the case of phosphorylation or dephosphorylation of the same protein (see Lastick and McConkey, 1980, as an example).…”