THE 3'-NONTRANSLATED REGION OF RAT RENAL GLUTAMINASE MESSENGER-RNA CONTAINS A PH-RESPONSIVE STABILITY ELEMENT

Rat kidney expresses two forms of glutaminase (GA) mRNA which probably result from the use of alternative polyadenylation signals. The two m RNAs are increased coordinately in response to metabolic acidosis via a mechanism that apparently does not involve transcriptional or transl ational regulation. A 956-bp fragment that contains the 3'-nontranslat ed sequence of the smaller CA cDNA was cloned into an expression vecto r (p beta G) that encodes a chimeric beta-globin growth hormone mRNA. Both the parent and the derived construct (p beta G-GA) were transfect ed into LLC-PK1-F+ cells. Stable transfectants express sixfold lower l evels of beta G-GA mRNA than that of the parent beta G mRNA. However, only the beta G-GA mRNA is increased 2.5-fold by growth in acidic medi um (pH 6.9, 10 mM HCO3-). The apparent half-life of the beta G mRNA (> 24 h) is unaffected by the pH. of the growth media. In contrast, the a pparent half-life of the beta G-GA mRNA is increased from 4.5 h to sim ilar to 24 h when cells are transferred to acidic medium for 8 h. The observed pH response is not reproduced when the beta G-GA construct is stably transfected into COS-7 cells or when a beta-globin-phosphoenol pyruvate carboxykinase chimeric gene is expressed in LLC-PK1-F+ cells. Thus the 3'-nontranslated region of the GA mRNA contains a pH-respons ive stability element.