From a partial Sau3Al library of Streptomyces coelicolor A3(2) DNA in ~11916, two hybrid plasmids pGXl and pGX2 were isolated that complemented S. coelicolor A3(2) or 5. lividans arginine auxotrophs. Subcloning DNA from pGXl in the Escherichia coli expression vector pRK9 containing the Serratia marcescens trp promoter gave rise to one plasmid, pZC2, that complemented E. coli argB, C , E and H auxotrophs, and another, pZC1, that complemented only the first three. The plasmids were markedly unstable in the various complemented hosts, to varying extents; pZCl was characterized further as providing the stablest hostlplasmid combinations. In vitro deletion of part of the vector's trp promoter did not affect complementation of the argB and C auxotrophs, implying that the 5. coelicolor A3(2) arg genes may be expressed from their own promoter. The trp promoter-less plasmids included isolates, such as pZCl77, that had suffered extensive further deletion without loss of complementing ability. Extracts of an E. coli argE auxotroph carrying pZC177 showed ornithine acetyltransferase activity, indicating that the complementing gene is of the argJ type. The complementation properties of in vitm deletion derivatives of pZC177 indicated the gene order argC-J-B. Part of argCand the upstream region were sequenced; an ORF was identified whose predicted product showed appreciable homology with the E. coli and Bacillus subtilis ArgC polypeptide. Upstream of this ORF a consensus-type promoter and ribosome binding site could be discerned; overlapping its promoter was a sequence with homology to arginine operators in these two other organisms.An in vitro frameshift in argC had a polar effect on expression in E. coli of argJ and B, suggesting that the three genes are transcribed in the same direction, possibly as an operon.
