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

For the elucidation of the age-dependent reduction of avidin synthesis in the oviduct of quails studies on on the level of post-transcriptional modification of mRNA were performed. Incorporation of [3H] adenosine into mRNA is drastically reduced in senescent animals compared to adult animals. Double labeling of mRNA with [3H]-adenosine and [3H] uridine revealed that in the presence of actinomycin D the incorporation ratio adenosine/uridine into mRNA increases to higher values in the case of adult animals compared with the ratio determined for mRNA from senescent animals. These data support the assumption that in senescent animals the length of the poly(A) sequence on mRNA might be shorter. Because of the low efficiency of label incorporation into poly(A) in whole animals, a method for directly introducing a radioactive label in vitro into the isolated poly(A) was developed for the estimation of the length of the poly(A) segments. A randomly labeled product with no apparent degradation is achieved by methylation of poly(A) with [3H] dimethyl sulphate. Therefore the method is a powerful tool for the detection and size determination of small amounts of poly(A). Size determination of poly(A) from oviducts of adult and senescent quails by the methylation method revealed that in the case of senescent animals an increase in shorter poly(A) tracts can be detected. These results support the assumption that the age-dependent reduction of avidin synthesis is also caused by changes in the control mechanisms on the post-transcriptional level.