TYPE-VI RNA IS THE MAJOR GAMMA-GLUTAMYL-TRANSPEPTIDASE RNA IN THE MOUSE SMALL-INTESTINE

Mouse gamma-glutamyl transpeptidase (gamma GT) is encoded by a single copy gene with at least five and probably six different promoters dire cting the transcription of six types of gamma GT RNAs. In mouse small intestine, only Type I, V, and VI gamma GT RNAs are detected, and ribo nuclease protection assays reveal that Type VI represents more than 90 % of gamma GT RNA. To investigate the structure of intestinal gamma GT RNA in greater detail, we cloned and sequenced mouse intestinal gamma GT cDNAs. Seven of eight informative clones were Type VI and consiste d of Type VI unique exons, VIa and VIb (as described previously by us) (Rajagopalan, S., Wan, D.-F., Habib, G. M., Sepulveda, A. R., McLeod, M. R., Lebovitz, R. M., and Lieberman, M. W. (1993) Proc. Natl. Acad. Sci. U. S. A. 90, 6179-6183) as well as common 3' sequences. Exon VIb contains two alternative splice accepters, one previously identified by us and the other 17 bases 5' of this site. Another clone contained a previously unidentified gamma GT mRNA designated as Type VII. Type V II consists of a unique 5' exon which is 315 base pairs upstream of th e exon VIa splice donor site and is spliced to exon VIb. Regulation of gamma GT expression in the small intestine is complex and involves at least three previously described promoters, alternative splicing, and a previously undescribed exonic sequence (Type VII RNA) 5' of promote r VI.