Gene organization and structure of the Streptomyces lividans gal operon

Abstract

Much of our present knowledge about gene regulation in bacteria is the result of work done on the gram-negative bacterium Escherichia coli and its various bacteriophages. More recently, gene regulation studies have expanded to include the differentiating Streptomyces species (22). These studies have focused on the isolation and characterization of genes involved in diverse cellular functions such as antibiotic resistance (7,52,53) and biosynthesis (10,16,18,28,36,37,48), carbon catabolism (19,22,45), and morphological differentiation (38). For example, some of the best-characterized of these genes are those which confer antibiotic resistance to neomycin (aph) and erythromycin (ermE). One notable feature of the aph and ermE genes is that each gene is controlled by tandem promoters which may act to differentially control gene expression (7,23). Among the most complex of the gene systems under study are those responsible for actinorhodin (28, 29) and methylenomycin (10) biosynthesis. Each gene system consists of clustered, multiple genes which are organized within polycistronic operons (10, 29). Our understanding of these operons is limited, however, since the molecular details of operon organization and the strategies used to temporally regulate their expression have yet to be revealed.One example of a multiple gene system whose regulatory strategies have been described is the Streptomyces lividans galactose utilization operon. We have recently demonstrated that expression of this operon is directed by two independently regulated promoters: galPi, which is responsible for galactose-dependent transcription of the operon, and galP2, which is an internal, constitutive promoter (19). As observed for the E. coli gal operon, glucose represses galactose induction of the S. lividans operon (19). Glucose repression in Streptomyces species, however, does not appear to be mediated by cyclic AMP (14, 35) but is controlled, at least in part, by glucose kinase (21). Thus, studies of the S. lividans gal operon should elucidate general features of Streptomyces operon organization and novel regulatory mechanisms used by this bacterium.In this report, the isolation, gene organization, and structure of the S. lividans gal operon are described. We demon-* Corresponding author. t Present address: Beckman Instruments, Inc., Brea, CA 92621. strated by complementation of E. coli gal mutants and DNA sequence analysis that the S. lividans gal genes are organized in the order galT, galE, and galK. The DNA sequence of the S. lividans gal genes was also used to predict the protein sequences for the Streptomyces gal enzymes. By comparing these protein sequences with the sequences of the corresponding E. coli (13,25) and Saccharomyces carlbergensis (11) gal enzymes, we found regions of structural homology within each of the galactose utilization enzymes. Finally, the relationship between the gene organization of the operon and the potential role played by the gal enzymes and their metabolites in Streptomyces physiology is discussed below. MATER...

Carbohydrate utilization in Streptococcus thermophilus: characterization of the genes for aldose 1-epimerase (mutarotase) and UDPglucose 4-epimerase

“…In many organisms, the genes for galactokinase (galK), UDPglucose 4-epimerase (galE), and UDPglucose-hexose-1-phosphate uridylyltransferase (gall) are present in a single operon, constituting the Leloir pathway for galactose metabolism (1,2,44). Alternatively, it has been shown for Erwinia stewartii that galE is not linked to galK and galT; rather, galE is linked to genes encoding enzymes involved in the biosynthesis of extracellular polysaccharides (13).…”

Galactose utilization in Lactobacillus helveticus: isolation and characterization of the galactokinase (galK) and galactose-1-phosphate uridyl transferase (galT) genes

“…Many organisms have the genes constituting the Leloir pathway for galactose metabolism, the galK, galT, and galE genes (the last coding for the uridine diphosphogalactose 4-epimerase), clustered or organized as one operon (1,2,50). L. helveticus, however, shows a clustering of only the galK and galT genes, which are followed downstream by a putative galM gene.…”

xylE functions as an efficient reporter gene in Streptomyces spp.: use for the study of galP1, a catabolite-controlled promoter

“…The Streptomyces lividans and S. coelicolor gal operons are well-characterized transcription units that may provide a relatively simple model for defining the way glucose repression is accomplished in these species (14). Transcription of gal is controlled by two independently regulated promoters: galPI, which is responsible for glucose-sensitive, galactose-dependent transcription of the entire operon, and galP2, a weak, constitutive promoter internal to the operon that directs transcription of galE and galK (1,14). We are interested in defining cis-acting sequences within or near galPI that are required for proper expression and regulation, and we are seeking to identify through mutational analysis genes encoding trans-acting factors that influence galPI utilization.…”