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Purine metabolism in neisseria meningitidis. 4. Interconversion of purine ribonucleotides
Abstract:
Radioactive hypoxanthine and adenine were readily incorporated into the nucleic acids (RNA + DNA) of the prototrophic strain M1 of Neisseria meningitidis with labelling of the purine bases adenine and guanine. Contrary to this, adenine was incorporated into the nucleic acids with labelling of adenine only in the purine mutant 6-1c which requires adenine and guanine for growth. Guanine was in both strains incorporated into the nucleic acids with labelling of the purine base guanine only. Crude meningococcal extracts from the prototrophic strain M1 and strain 6-1b requiring histidine, proline, adenine and guanine for growth (his pro A G) were found to have activities corresponding to adenylosuccinate synthetase (EC 6.3.4.4), adenylosuccinate lyase (EC 4.3.2.2.), inosine 5'-phosphate dehydrogenase (EC 1.2.1.14)) and guanosine 5'-phosphate synthetase (EC 6.3.5.2). This last enzyme was active also with (NH4)2SO4 as amino donor. No activity corresponding to guanosine 5'-phosphate reductase (EC 1.6.6.8) could be demonstrated in either strain. The findings show that the mutant strains 6-1b and 6-1c are both blocked between aminoimidiazolcarboxamide ribonucleotide (AICA-R) and inosine 5'-phosphate (IMP). Transformation experiments with mutants requiring adenine and guanine for growth indicate that the negative property of these mutants is due to a lesion in one genetic locus or at least in loci that are very closely linked.
Insights
Neisseria meningitidis mutants unable to synthesize purines were identified. These mutants are blocked in the pathway between aminoimidiazolcarboxamide ribonucleotide and inosine 5'-phosphate, indicating a genetic defect.
Area of Science:
- Microbiology
- Biochemistry
- Genetics
Background:
- Neisseria meningitidis requires purines for nucleic acid synthesis.
- Understanding purine biosynthesis pathways is crucial for microbial genetics and drug development.
Purpose of the Study:
- To investigate purine metabolism in Neisseria meningitidis.
- To identify genetic blocks in purine auxotrophic mutants.
Main Methods:
- Utilized radioactive labeling to trace purine incorporation into nucleic acids.
- Assayed enzyme activities involved in purine biosynthesis.
- Performed genetic transformation experiments with purine auxotrophic mutants.
Main Results:
- Prototrophic strain M1 incorporated radioactive hypoxanthine and adenine into adenine and guanine bases.
- Purine mutant 6-1c incorporated adenine only into adenine.
- Mutants 6-1b and 6-1c showed a block between aminoimidiazolcarboxamide ribonucleotide and inosine 5 omino-phosphate.
- Transformation experiments suggested a single genetic locus or closely linked loci are responsible for the defect.
Conclusions:
- Neisseria meningitidis mutants 6-1b and 6-1c are blocked in the purine biosynthesis pathway.
- The genetic defect is likely located in a single or closely linked genetic locus.