Multicopy suppression by asd gene and osmotic stress-dependent complementation by heterologous proA in proA mutants.

Auxotrophic proA mutants of Escherichia coli were complemented by two different classes of Corynebacterium glutamicum genes. One of these was the asd gene. The E. coli asd gene also complements the same proA alleles. Complementation of proA by the asd+ gene requires a high asd dosage and the proB and the proC gene products. The reciprocal complementation pattern (asd by the proA+ gene) was not observed. This complementation appears to be due to multicopy suppression by a proline biosynthetic gene whose product was expected to play a negligible role in this pathway. The other class of complementing clones carries the C. glutamicum proA gene. Complementation of E. coli proA mutants by the C. glutamicum proA+ gene was optimal at high osmolarity.