Processing of high molecular weight ovalbumin and ovomucoid precursor RNAs to messenger RNA

The existence of poly(A) sequences in the multiple high molecular weight forms of ovalbumin and ovomucoid nuclear RNA has been determined. The results indicate that all the bands observed in the total nuclear RNA including the largest (7.8 kb) were also detected in the poly(A) RNA. Kinetic labeling and chase experiments in oviduct tissue-suspension system indicated that the ovalbumin and ovomucoid high molecular weight RNAs which were labeled with a short-time incubation can be chased by cold nucleosides and actinomycin D into mature mRNAs. The largest RNAs labeled in this oviduct suspension system have a size of 7.8 kb for ovalbumin and 5.5 kb for ovomucoid, which correspond respectively to the "a" bands of steady state RNA. The processing of the precursors to mature mRNA was also examined by electron microscopic analysis, by hybridizing oviduct nuclear RNA to probes which were isolated from different segments of intervening DNA sequences and by measuring the turnover kinetics of specific intervening sequences present in cellular poly(A) RNA. The results indicate that the seven intervening sequence regions of the ovomucoid precursor are removed in a preferred but not necessarily an obligatory order.