Type VI RNA is the major γ-glutamyl transpeptidase RNA in the mouse small intestine

Mouse γ-glutamyl transpeptidase (γGT) is encoded by a single copy gene with at least five and probably six different promoters directing the transcription of six types of γGT RNAs. In mouse small intestine, only Type I, V, and VI γGT RNAs are detected, and ribonuclease protection assays reveal that Type VI represents more than 90% of γGT RNA. To investigate the structure of intestinal γGT RNA in greater detail, we cloned and sequenced mouse intestinal γGT cDNAs. Seven of eight informative clones were Type VI and consisted 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 acceptors, one previously identified by us and the other 17 bases 5' of this site. Another clone contained a previously unidentified γGT mRNA designated as Type VII. Type VII consists of a unique 5' exon which is 315 base pairs upstream of the exon VIa splice donor site and is spliced to exon VIb. Regulation of γGT 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 promoter VI.