Abstract
Two independent cDNA clones encoding fructose 6-phosphate, 2-kinase/fructose 2, 6-bisphosphatase were isolated from a human placental cDNA library. The deduced amino acid sequences showed that one of the clones, 2K-1, was almost identical to the rat testis isozyme and the other, 2K-3, was different from any known isozymes expressed in mammalian tissues. The results of Southern blot analysis suggested that clones 2K-1 and 2K-3 were encoded as single copy genes and located in different parts of the genome. Since open reading frames of the cDNA clones were not complete, we obtained the 5'-end of the clone 2K-3 cDNA using the 5'-rapid amplification of cDNA end method. The entire cDNA (HP; 1, 756bp) had a coding capacity of 519 amino acids (Mr=59, 410), and putative phosphorylation sites for protein kinases A and C on the C terminus. Northern blot analysis using a fragment of the HP as a probe showed that a major band of 5.4kb, significantly different in size from known isozyme mRNAs such as liver (2.1kb), muscle (1.9kb), heart (4.0kb), and testis (2.0kb), was present in poly (A)+RNA preparations of human first trimester and term placentae. These results strongly suggested that this 5.4kb mRNA codes a novel isozyme of fructose 6-phosphate, 2-kinase/fructose 2, 6-bisphosphatase.
