Age-dependent gene induction in quail oviduct X. Alterations on the post-transcriptional level (enzymic aspect)

In quail oviducts the rate of synthesis of avidin, the biological end-point marker for the molecular events caused by progesterone, decreases with age. The cause of the reduced capacity of avidin induction has been studied on the molecular biological level of polyadenylation of RNA which is one step in the process of post-transcriptional modification of heterogeneous nuclear RNA resulting in the formation of functional mRNA molecules. This novel approach was biochemically possible after the discovery of the poly(A) anabolic enzyme (poly(A) polymerase) and the two poly(A) catabolic enzymes (endoribonuclease IV and 5′-exoribonuclease). These enzymes are involved in the synthesis and degradation of the poly(A) segment of mRNA in vitro and most likely also in poly(A) metabolism in intact cell systems. Enzymatically controlled poly(A) metabolism of mRNA is regulated by the following interrelations: poly(A)-associated proteins and endoribonuclease IV; labilizing factor and poly(A)-associated proteins; 5′-exoribonuclease in cooperation with endoribonuclease IV and poly(A) polymerase. A close correlation between high levels of poly(A) catabolic enzymes and low rate of protein synthesis which was established in cell culture systems, seems also to be partially the biochemical cause for the reduced avidin synthesis in aging quail oviduct.