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

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The maize chloroplast gene for the β subunit ( atpB)of the chloroplast cf 1 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 β-galactosidase or with bacteriophage λ 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 une mutants that are defective in binding of the F 1 ATPase component to the Fo 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 β subunit are involved in binding to the E. coli inner membrane, and that this binding is probably mediated by the bacterial F 0receotor.