MOLECULAR-CLONING AND NUCLEOTIDE-SEQUENCE OF A PUTATIVE TRPDC(F)BA OPERON IN BUCHNERA-APHIDICOLA (ENDOSYMBIONT OF THE APHID SCHIZAPHIS-GRAMINUM)

A 8,392-nucleotide-long DNA fragment from Buchnera aphidicola (endosymbiont of the aphid Schizaphis graminum) contained five genes of the tryptophan biosynthetic pathway [trpDC(F)BA] which code for enzymes converting anthranilate to tryptophan. These genes are probably arranged as a single transcription unit. Downstream of the trp genes were ORF-V, ORF-VI, and P14, three open reading frames which in Escherichia coli are also found downstream of the trp operon. Upstream of the B. aphidicola trp genes were two unidentified open reading frames, one of which potentially codes for a membrane-spanning protein with a leader sequence. Evidence for the presence of trpB in the endosymbionts of eight additional species of aphids and two species of whiteflies was obtained. These results as well as those of A. E. Douglas and W. A. Prosser (J. Insect Physiol. 38:565-568, 1992) suggest that aphid endosymbionts are capable of synthesizing tryptophan, which is required by the aphid host.