The galactose operon of E. coli K-12. II. A deletion analysis of operon structure and polarity.

PREVIOUS genetic studies have conclusively established the order of the three structural genes in the galactose operon to be epimerase-transferasekinase (see Figure 1 ) ( ADLER and KAISER 1963; BUTTIN 1963b; ADLER and TEMPLETON 1963). The elegant work of ADLER and TEMPLETON (1963) and subsequently of KAYAJANIAN (1965), DAVISON, FRAME and BISHOP (1967), and PFEIFFER and OELLERMAN ( 1967) have demonstrated the feasibility of high-resolution deletion mapping of the kinase and transferase structural genes by the use of xdg transducing particles which carry partial galactose operons. However, because only transducing particles carrying an intact, active epimerase gene can be isolated and purified, they cannot be used to map the epimerase end of the operon. Both biochemical (MICHAELIS and STARLINGER 1968) and genetic (ADHYA and SHAPIRO 1969) data suggest that reading of the galactose operon proceeds from the epimerase end and that there exist one or more non-structural, regulatory elements in which mutations can lead to reduction or abolition of the activity of all three genes of the galactose operon. Hence, the need for a complete and detailed map of the galactose operon, in particular the epimerase gene, is clear. In this communication we shall present such a map based on the use of transducing phage and bacterial deletions. Our results confirm our previous conclusion on the epimerase to kinase polarity of the galactose operon and show that essential and ratelimiting regulatory elements are located at the epimerase end.