Rat muscle fructose-1,6-bisphosphatase: Cloning of the cDNA, expression of the recombinant enzyme, and expression analysis in different tissues

The 1282 bp cDNA of an isoenzyme of fructose-1,6-bisphosphatase was cloned from rat muscle. It shows 70% positional identity to the cDNA of rat liver fructose-1,6-bisphosphatase and is clearly the product of a gene different from that coding for the liver enzyme. After cloning of the coding region of the rat muscle fructose-1,6-bisphosphatase cDNA in an expression vector, the recombinant enzyme could be detected in E. coli cell-free extracts by activity determination and Western blotting. Overexpressed fructose-1,6-bisphosphatase was found to be allosterically inhibited by AMP comparably to the enzyme isolated from rat muscle. Analysis of steady-state mRNA levels of various rat tissues with reverse-transcriptase polymerase chain reaction (RT-PCR) and Northern blotting revealed one or the two fructose-1,6-bisphosphatase isoenzyme mRNAs in most tissues tested with significant quantitative differences. Quantitative PCR using a homologous competitor showed that 1 mu g of total RNA of rat muscle contains 1.7 x 10(6) molecules of rat muscle fructose-1,6-bisphosphatase mRNA. 3 x 10(4) copies of this message were found per mu g total RNA of heart and kidney, respectively.