Synthesis of maize chloroplast ATP-synthase beta-subunit fusion proteins in Escherichia coli and binding to the inner membrane.

The maize chloroplast gene for the beta subunit (atpB) of the chloroplast CF1 component of ATPase from maize, when fused to either the lacZ or ral genes in the vectors pMC1403 or pHUB4, is expressed in Escherichia coli as a fusion protein with beta-galactosidase or with bacteriophage lambda Ral sequences. Some of the fusion proteins are converted to a membrane-bound form, as determined by differential and sucrose-gradient centrifugation. The specificity of membrane binding has been examined using E. coli unc mutants that are defective in binding of the F1 ATPase component to the F0 receptor site on the membrane, and by the use of two different length maize atpB::lacZ gene fusions. We show that the first 365 N-terminal amino acids (aa) of the maize beta subunit are involved in binding to the E. coli inner membrane, and that this binding is probably mediated by the bacterial F0 receptor.