Abstract
Somatic cell hybrids obtained from the fusion of human B lymphocytes and an asparagine synthetase-deficient Chinese hamster ovary cell line were isolated after growth in asparagine-free medium. The human and hamster forms of asparagine synthetase differ significantly in their rate of inactivation at 47.5 degrees C. The asparagine synthetase activity expressed in the hybrids was inactivated at 47.5 degrees C at the same rate as the human form of the enzyme. Karyotypic analysis and analysis for chromosome-specific enzyme markers showed that the structural gene for asparagine synthetase is located on chromosome 7 in humans. The heat-inactivation profile for asparagine synthetase in extracts of hybrids formed between human peripheral leukocytes and a hamster cell line expressing asparagine synthetase activity was intermediate between the two parental types when human chromosome 7 was present, but was identical to the hamster parent when chromosome 7 was absent.
Highlights
Asparagine synthetase catalyzes the ATP-dependent synthesis of asparagine from aspartic acid and glutamine in higher eukaryotes [1]
Our results indicate that these hybrids are producing the human asparagine synthetase and that the structural gene for asparagine synthetase is on chromosome 7
The asparagine synthetase activity in all 5 primary hybrid clones isolated resembles the human variety in its heat sensitivity
Summary
Asparagine synthetase catalyzes the ATP-dependent synthesis of asparagine from aspartic acid and glutamine in higher eukaryotes [1]. Waye and Stanners have isolated a mutant of Chinese hamster ovary cells which lacks asparagine synthetase activity and requires asparagine in the medium for growth [12]. The phenotype of this mutant is recessive in intraspecific cell hybrids. This mutational auxotrophy should make it possible to isolate human-hamster hybrids able to grow in medium lacking asparagine because of the presence of the human gene for asparagine synthetase. Our results indicate that these hybrids are producing the human asparagine synthetase and that the structural gene for asparagine synthetase is on chromosome 7
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