Localization of DNA sequences governing alternative mRNA production of rat kininogen genes.

The two types of the rat kininogen genes show different modes of mRNA production. The K gene encodes two distinct mRNAs for high molecular weight (HMW) and low molecular weight (LMW) kininogens. These two mRNAs are generated by differential usage of the 3'-terminal exon (LMW exon) and the one next to this exon (HMW exon) through alternative polyadenylation and splicing. In contrast, the two T genes selectively generate the LMW form of the mRNA, although the T genes are extremely homologous to the K gene, including the sequence (psi HMW region) corresponding to the HMW exon of the K gene. In this study, we constructed a series of chimeric kininogen genes by exchanging equivalent restriction fragments of the K and T genes and examined the sequences and the mechanisms governing the different expression patterns of the kininogen genes by introducing the chimeric genes into heterologous COS cells. The results indicate that the formation of the two forms of the mRNA is controlled by two separate 3' sequences of the kininogen genes. One is located within the internal sequence of the HMW/psi HMW region, whereas the other is within the LMW exon and its preceding region. Our data also suggest that the different expression patterns of the kininogen genes are primarily governed by differing splicing efficiency.