The Use of Cloned nif Regulatory Elements from Klebsiella pneumoniae to Examine nif Regulation in Azotobacter vinelandii

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Abstract
Summary: Regulatory genes controlling nif expression and also nif promoters fused to lacZ from Klebsiella pneumoniae were cloned on wide-host-range plasmids and introduced into Azotobacter vinelandii to compare regulation of nif expression in the two organisms. A low-copy-number plasmid carrying K. pneumoniae nif A corrected an A. vinelandii Nif-regulatory mutation, whereas a plasmid carrying ntrC did not. A high-copy-number plasmid carrying K. pneumoniae nifL eliminated nif expression in K. pneumoniae but not in A. vinelandii. K. pneumoniae nifL- and nifF-lacZ fusions were expressed strongly in A. vinelandii and were not repressed by ammonium. A nifH-lacZ fusion was not expressed in any conditions in this background except very weakly when K. pneumoniae nifA was also present. The implications of these findings are discussed.

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