MOLECULAR CLONING OF HUMAN UMP SYNTHASE

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In order to clarify the cause of hereditary orotic aciduria, UMP synthase (a multifunctional protein having both orotate phosporibosyltransferase and OMP decarboxylase activities) was purified from normal human erythrocytes. The enzyme protein had a molecular weight of 51,000. Then a cDNA fragment of mouse OMP decarboxylase was isolated from a <lambda>gtll mouse spleen cDNA library by the use of a synthesized oligonucleotide probe. Screening of a <lambda>gtll human placenta cDNA library yielded two positive clones which hybridized strongly to the mouse cDNA fragment. Analysis of the nucleotide sequence of the entire cDNA insert (1.7 kb) of one of the clones indicated that it contained an open reading frame (1,444 bp) encoding a protein with a molecular weight of 52,000. The deduced amino acid sequence of the 3'-half of the insert showed 89% homology with that deduced from Ehrlich ascites carcinoma OMP decarboxlase cDNA. Northern blot analysis revealed a presence of a single band of approximately 1.8 kb, which suggests that the cloned cDNA contains the whole message for human UMP synthase.