STABILITY OF RNA SYNTHESIZED BY MOUSE OOCYTE DURING ITS MAJOR GROWTH PHASE

The RNA of growing mouse oocytes and ovulated ova was labeled by injection of a solution containing tritiated uridine into the ovarian bursa. The time course of incorporation into RNA by oocytes was followed by analysis of alkali-labile acid insoluble radioactivity and by autoradiography. Most of the incorporation into RNA by growing oocytes took place within 1 day of bursal injection of the precursor, reflecting the rapid fall of label in the acid soluble precursor pool. The RNA of growing oocytes of all sizes was unusually stable, at least 80% of the labeled RNA present 2 days after bursal injection being retained until ovulation 10-20 days later. The fraction of heterogeneous RNA in labeled RNA of ova was estimated as 20% by sucrose gradient analysis. Egg RNA is apparently synthesized primarily during the period of oocyte growth 1-2 wk before ovulation.