CHAPERONINS AS POTENTIAL GENE REGULATORY FACTORS - IN-VITRO INTERACTION AND SOLUBILIZATION OF NIFA, THE NIF TRANSCRIPTIONAL ACTIVATOR, WITHGROEL

A previous study (Govezensky, D., Greener, T., and Zamir, A. (1991) J. Bacteriol, 20, 6339-6346) indicated that the chaperonin GroEL was req uired for maximal expression from nif promoters in Klebsiella pneumoni ae and nif-transformed Escherichia coli. That this requirement stemmed from the ability of GroEL to properly fold NifA, the nif transcriptio nal activator, was first supported by co-immunoprecipitation of NifA i n K. pneumoniae extracts with anti-GroEL antibodies. In the present in vitro study, NifA, partially purified from E. coli overexpressing the protein, was diluted from a 6 M urea solution into a refolding buffer in the presence or absence of GroEL. Dilution in the absence of GroEL caused the complete precipitation of NifA. When present in the diluti on buffer, GroEL bound NifA and maintained it in a soluble state. GroE L was also found to bind NifA newly synthesized in an in vitro transla tion system. For both NifA preparations, cochaperonin GroES and ATP pr omoted release of NifA from GroEL. These results provide evidence for the association of NifA with GroEL and for the role of both GroEL and GroES in the solubilization and thereby folding of the nif transcripti onal activator.