Organisation, Potential Regulatory Elements and Evolution of trp Genes in Acinetobacter

Abstract

This article discusses the evolutionary and regulatory implications derived from the nucleotide sequence of trp genes from Acinetobacter calcoaceticus. The genetics of tryptophan biosynthesis have been studied in a wide variety of organisms (Crawford, 1989). As depicted in Fig. 1, organisation of trp genes differs considerably among the prokaryotes studied so far. For instance, Escherichia coli has five genes in a single operon for tryptophan biosynthesis (Yanofsky et al., 1981), Bacillus subtilis has six genes in a single operon (Henner et al., 1984) and A. calcoaceticus has seven genes in three unlinked clusters (Sawula and Crawford, 1972, 1973). Unlinked clusters of trp genes have also been reported in Pseudomonas aeruginosa, P. putida (Holloway et al., 1979; Shinomiya et al., 1983) and Rhizobium meliloti (Johnston et al., 1978). Sequence information is available for trp genes from E. coli (Yanofsky et al., 1981), B. subtilis (Henner et al., 1984), R. meliloti (Bae et al., 1989), P. putida (Crawford and Eberly, 1989; Essar et al., 1990a) and P. aeruginosa (Crawford et al., 1986; Essar et al., 1990b). From A. calcoaceticus the trpGDC operon (Kaplan et al., 1984), the trpE gene (Haspel et al., 1990) and the trpFB operon (Ross et al., 1990; Kishan and Hillen, in preparation) have been sequenced. Using a newly developed shuttle vector (Hunger et al., 1990) for A. calcoaceticus, the promoter structures of the trpE and trpFB genes have been determined. This article compares the organisation of trp genes in A. calcoaceticus with that in other organisms and discusses potential common regulatory sequences for their expression. Striking similarities of trp genes from P. putida and A. calcoaceticus with respect to these features are presented and discussed.