Fig. 8.

Differential splicing of the OT and VP pre-RNAs. From the relative steady-state levels of the mRNAs and hnRNAs found in the SON for the oxytocin (Fig. 5) and vasopressin (Fig. 6) genes, we deduced a speculative kinetic pattern of splicing. The K symbols represent theoretical rate constants, the actual values of which are unknown, and their associated numbers indicate the presumed order of splicing (see discussion). The OT primary transcript first has intron 1 excised out, thereby producing an intermediate, which only contains OT intron 2. OT intron 2 is subsequently excised, leading to the OT mRNA. In contrast, in the VP gene, intron 2 is first excised, followed by the removal of intron 1, thereby producing the VP mRNA. The most important distinction in splicing patterns between the OT and VP pre-mRNAs is the apparent accumulation of intron 2-containing hnRNA intermediate in the OT splicing process.