Regulation of macromolecular synthesis during hyphal germ tube emergence from Mucor racemosus sporangiospores

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Abstract
Protein and RNA syntheses were examined during hyphal germ tube emergence from sporangiospores of a dimorphic phycomycete, M. racemosus. Both classes of macromolecules were synthesized upon introduction of the dormant sporangiospores into nutrient medium. The specific rates of synthesis of both protein and RNA accelerated during initial germ tube emergence and reached a maximum when the emergence of new germ tubes ended. The specific rates of synthesis later decreased during further hyphal elongation. The distribution of ribosomes between active polysomes and monosomes and inactive subunits was determined by sucrose density gradient centrifugation, and the rate of amino acid addition to nascent polypeptide chains was calculated throughout the developmental sequence. Both the percentage of ribosomes active in protein synthesis and the velocity of ribosome movement along the mRNA were continuously adjusted throughout hyphal germ tube development. The free intracellular amino acid pools were measured throughout development. Alanine, glutamate and aspartate were present at very high concentrations in the dormant spores but were rapidly depleted during hyphal germ tube emergence. Hyphal germ tube development from yeast cells of Mucor and dormant spores of other fungal species was discussed.