Genetic engineering offers the potential for creating new proteins with novel materials properties. The aim of this study is to develop strategies for incorporating the non-natural amino acid p-fluorophenylalanine (pfF), which is known to be utilized by the Escherichia coli protein synthesis apparatus, into repetitive polypeptides. pfF has been successfully incorporated into target protein by in vivo substitution of pfF for phenylalanine in a phenylalanine auxotroph of the E. coli BL21(DE3 expression strain containing a chromosomal copy of the bacteriophage T7 RNA polymerase gene under LacUV5 promoter control. The auxotroph was generated by transposon mutagenesis using P1-mediated transduction. The repetitive protein -[(Ala-Gly)3.pfF.Gly]13- (1) was expressed from an artificial gene under T7 promoter control. Expression of 1 was carried out by shifting the host culture to pfF-containing medium after induction of T7 RNA polymerase for 10 min with isopropyl beta-D-thiogalactopyranoside in medium containing the 20 natural amino acids. Replacement of 95-100% of phenylalanine by pfF was confirmed by H-1 NMR spectroscopy and amino acid analysis. Fourier transform infrared spectroscopy and X-ray scattering suggest that both 1 and the phenylalanine variant (2) adopt antiparallel beta-sheet structures in the solid state.