Pattern of ribonucleic acid synthesis during germination of Allomyces macrogynus mitospores

Abstract

The relationship between ribonucleic acid (RNA) synthesis and germination of Allomyces macrogynus mitospores was investigated. It was determined that the synthesis of all classes of RNA was initiated during the first 10 min of germination, around the time of encystment. It is during this stage that the membrane of the nuclear cap structure begins to break down, dispersing the cell complement of ribosomes throughout the cytoplasm. After encystment, there was an increase in the rate of synthesis of the four stable RNA species (4S, 5S, 19S, and 27S) which leveled off as the germ tube emerged. Data suggested that messenger RNA was synthesized at an increasing rate during the course of germination. Studies of RNA precursor pool behavior and RNA synthesis in the presence and absence of actinomycin D indicated that no species of RNA, including messenger RNA, was synthesized in the presence of actinomycin D. Further, precursor pool measurement indicated that the apparent increase in the rate of RNA synthesis during germination was largely due to increased specific activity of the RNA precursor pool.

Protein synthesis during germination of Allomyces macrogynus mitospores

“…These and previous results (14,15) indicate that the mitospore of A. macrogynus contains its own developmental program for the early protein synthesis of germination. In contrast to newly synthesized RNA, the protein(s) made during the early stages of germination examined in this work is an absolute requirement for emergence of the germ tube, as evidenced by the fact that development of the spore beyond the stage [3Hlleucine-pulse-labeled polysomes.…”

“…The mRNA was found to be associated with polysomes and was not synthesized during the period of sporogenesis, suggesting that it was derived from mRNA already present in sporangia. We further established that the germination of A. macrogynus spores is independent of the concomitant synthesis of new mRNA (15).…”

“…Maintenance of vegetative cultures ofA. macrogynus and conditions for the preparation of mitospores and their synchronous germination have been described previously (4,15).…”

“…When A. macrogynus spores are germinated in the presence of 10 ,ug of actinomycin D (Act D) per ml, their development proceeds through encystment to the rhizoid stage (15). In the presence of 2 ,ug of cycloheximide per ml, the germination process is sharply arrested in the encystment stage.…”

“…The inhibition of protein synthesis by cycloheximide during germination of A. macrogynus spores was demonstrated by the determination that no radioactivity above background was incorporated at any period of germination examined in cells pulse-labeled with [3H]leucine during germination in the presence of 2 mg of cycloheximide per ml. Studies of germination in the presence of Act D have demonstrated that no new RNA synthesis is required (15). The question arises as to whether protein synthesis occurs in the presence of Act D (Table 1).…”