The Genetic Basis of ASase Deficiency
During the past 2 years, our goal has been to clone all of the enzymes of vertebrate de novo purine synthesis by functional complementation of microbial auxotrophic mutants. We employed an avian liver cDNA expression library excised as phagemids from the bacteriophage λvector λZAP-II. We reasoned that the mRNA levels in avian liver would be elevated because, lacking a urea cycle, avian systems use purine biosynthesis for ammonia excretion. We and others have isolated vertebrate cDNAs encoding 11 of the 14 activities in the pathway by this methodology [1–5]. With this method, we were unable to isolate clones encoding the first and fourth enzymatic steps leading from PRPP to IMP. We were also unable to isolate a clone encoding adenylosuccinate synthetase.
KeywordsUrea Codon EDTA Lactate Catalysis
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