Reconstitution of plant nitrate reductase by Escherichia coli extracts and the molecular cloning of the chlA gene of Escherichia coli K12.

Extracts from Escherichia coli, wild type and chlB, chlC, chlD, chlE, and chlG, but not chlA mutants, were able to reconstitute the nitrate reductase activity in Nicotiana tabacum cnx68 and Hyoscyamus muticus MA-2 mutant extracts. Because cnx68 and MA-2 lack the molybdenum cofactor required for nitrate reductase activity, these results indicate that the functional chlA gene is essential to produce the molybdenum cofactor in E. coli. A clone containing a gene capable of complementing the chlA mutation SA493 was obtained on a large cosmid pJT1. A 1.9 kb BclI fragment subcloned from pJT1 in the vector plasmid pBR322 was shown to complement the chlA SA493 mutant when inserted in either of the two possible orientations. This suggested that the chlA gene was contained intact, including its own promoter, on the 1.9 kb BclI fragment.