Regulation of gene expression during aerobic germination of Mucor racemosus sporangiospores.

The pool of mRNA stored in dormant sporangiospores of Mucor racemosus and expressed during early germination in air has been investigated. Total RNA was extracted from dormant and germinating spores and translated in a cell-free rabbit reticulocyte system containing L-[35S]methionine. Isotopically labelled in vitro translation products were analysed by PAGE and autoradiography and were compared with labelled proteins synthesized in vivo at the same stages of development. This comparison revealed several significant findings about the fates of individual mRNA populations as templates in translation: (i) a pool of mRNA, presumably represented entirely or in part by a recoverable polyadenylated RNA fraction, can be extracted from dormant spores in a translatable form; (ii) most of the differential gene expression displayed at the level of protein synthesis during germination results from concomitant changes in functional mRNA levels; (iii) some of the stored mRNA species may be activated and others inactivated by post-transcriptional processing mechanisms; and (iv) a small population of gene products may be regulated at the level of selective translation of pre-existing messages.