Two promoters, one inducible and one constitutive, control transcription of the Streptomyces lividans galactose operon.

Abstract

Galactose utilization in Streptomyces lividans was shown to be controlled by an operon that is induced in the presence of galactose and repressed by glucose. Two promoters, gaIPi and galP2, which direct transcription of two distinct polycistronic transcripts, have been identified. galPI is located immediately upstream of the operon and is induced in the presence of galactose. This promoter directs transcription of the gaiT, gaIE, and galK genes. The second promoter, gaLP2, is located within the operon just upstream of the gaIE gene. This promoter is responsible for constitutive transcription of the galE and galK genes. Comparison of the S. lividans gal operon to the Escherichia coli gal operon indicates the presence of a constitutive promoter positioned upstream of galE in both operons. We suggest that coupling the operon's constitutive promoter to the galE gene fulfills a physiological requirement for constitutive UDPgalactose 4-epimerase expression in Streptomyces.The coordinate activation of sets of genes often involves complex combinations of regulatory signals. Many basic concepts about the mechanisms of gene expression in bacteria were formulated from work with the carbon catabolic and amino acid biosynthetic operons of Escherichia coli (1, 2). There are, however, many organisms that utilize different regulatory mechanisms to accomplish the same metabolic events. For example, the genes responsible for galactose utilization in E. coli are organized within a polycistronic operon. The operon is transcribed from two overlapping promoters, PI and P2. The PI promoter is positively activated by a cAMP-receptor protein, whereas P2 is repressed upon PI activation. Both promoters are negatively regulated by the gal repressor (3). The galactose utilization genes of Saccharomyces cerevisiae are also clustered and coordinately expressed. However, each gene is transcribed from its own promoter. The promoters are negatively controlled by the gal80 gene product and positively activated by the gal4 gene product (4). As in E. coli, galactose utilization in Sa. cerevisiae is subject to catabolite repression. Catabolite repression in Sa. cerevisiae, however, is not mediated by cAMP but by the hexokinase isoenzyme PII (5, 6). Thus, the processes that control gene activation reflect both the unique biology of individual organisms and universal principles of gene expression.We are interested in gene regulation in the Gram positive, differentiating bacterium Streptomyces. Members of this genus express a variety of interesting gene sets including those responsible for its morphological differentiation (7) and the biosynthesis of antibiotics (8, 9). We have chosen to study the galactose utilization operon as an example of a regulated set of genes in Streptomyces lividans because it is subject to glucose repression (10) and galactose induction (11). This paper describes the isolation and characterization of the promoters that direct transcription of the St. lividans gal operon. We demonstrate that the St. lividans galactose ...

Sequence and transcriptional analysis of the Streptomyces glaucescens tcmAR tetracenomycin C resistance and repressor gene loci

“…This observation is explored further in the accompanying paper (20). The presence of two promoters, one of which is inducible and one of which is constitutive, has been reported previously in the case of the S. lividans galactose operon (16,57). We note that the close proximity of the transcriptional and probable translational start sites for the tcmR-pl mRNA is unusual, but similar configurations have been reported for other Streptomyces genes.…”

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

“…Catabolite control in all gram-positive bacteria is poorly understood and is of particular interest in Streptomyces species because of its influence on the expression of antibiotic biosynthesis genes (26) and extracellular enzymes (18,37). 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).…”

“…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.…”

“…The resulting plasmid, pJW1, was digested with HindIII and EcoRI to generate a 5.9-kilobase fragment that was ligated to the 11.2-kilobase HindIII-EcoRI fragment from pMB158 (as for construction of pXE4). Plasmid pK21galP2 has been described previously (14).…”

Cloning and Sequencing of the Gene which Encodes the Highly Inducible Acetamidase of Mycobacterium Smegmatis

“…Two direct repeat sequences, TCACCGCCG and GCGCCGTC, upstream of the amidase gene are shown in Fig. 6; direct repeats have been found at the inducible promoter site of the galactose operon in Streptomyces lividans, but their role in induction is unknown (Fornwald et al, 1987).…”