Regulation of the processing of glucose-6-phosphate dehydrogenase mRNA by nutritional status.

Expression of glucose-6-phosphate dehydrogenase (G6PD) gene during starvation and refeeding is regulated by a posttranscriptional mechanism occurring in the nucleus. The amount of G6PD mRNA at different stages of processing was measured in RNA isolated from the nuclear matrix fraction of mouse liver. This nuclear fraction contains nascent transcripts and RNA undergoing processing. Using a ribonuclease protection assay with probes that cross an exon-intron boundary in the G6PD transcript, the abundance of mRNAs that contain the intron (unspliced) and without the intron (spliced) was measured. Refeeding resulted in 6- and 8-fold increases in abundance of G6PD unspliced and spliced RNA, respectively, in the nuclear matrix fraction. However, the amount of G6PD unspliced RNA was at most 15% of the amount of spliced RNA. During refeeding, G6PD spliced RNA accumulated at a rate significantly greater than unspliced RNA. Further, the amount of partially spliced RNA exceeded the amount of unspliced RNA indicating that the enhanced accumulation occurs early in processing. Starvation and refeeding did not regulate either the rate of polyadenylation or the length of the poly(A) tail. Thus, the G6PD gene is regulated during refeeding by enhanced efficiency of splicing of its RNA, and this processing protects the mRNA from decay, a novel mechanism for nutritional regulation of gene expression.