THE EFFECT OF OCHRE SUPPRESSION ON MEIOSIS AND ASCOSPORE FORMATION IN SACCHAROMYCES

[摘要] The effect of altered tyrosyl-tRNAs on the developmental process of sporulation was examined. Mutations in eight independent loci resulting in tyrosine-inserting nonsense suppressors were tested for their effects on sporulation. Different levels of inhibition were found ranging from SUP3 - o , which caused the greatest reduction of sporulation (7-17% of wild type), to SUP11 - o which caused no reduction in sporulation. Since the SUP3 - o mutation exhibited the greatest effect, it was studied in detail. Although SUP3 - o is a dominant nonsense suppressor, its effect on sporulation is recessive. Expression of the sporulation deficiency is dependent upon the stage of transfer from glucose growth medium ( i.e ., log, early stationary, etc.) to sporulation medium. SUP3 - o / SUP3 - o diploid cells transferred from log or early stationary phase are capable of sporulation, whereas cells transferred after early stationary phase ( i.e ., after adaptation to respiration) exhibit poor sporulative ability. Sporulation events were examined under restrictive conditions to observe those events completed by SUP3 - o / SUP3 - o diploids. The early events of sporulation occur in these cells. Later events are completed by progressively fewer cells. Premeiotic DNA synthesis occurred in approximately 40% of the cells, nuclear segregation occurred in 20%, and finally, only 2% formed asci. The fact that fewer late-sporulation events occur under restrictive conditions can be explained by increased efficiency of suppression.

[学科分类] 医学（综合）