Control of cloned gene expression by promoter inversion in vivo: construction of the heat-pulse-activated att-nutL-p-att-N module

We have constructed a prototype of gene-expression plasmids with three novel properties: its "OFF phase" is absolute in all common hosts because the expression promoter is facing away from the studied gene and is blocked by a strong terminator; the "ON phase" is attained by the rapid and efficient inversion of the promoter; only a short heat pulse or exposure to other inducing agents is required to initiate this two-stage process. In the first stage, synthesis of the phage lambda Int protein is induced by the transient derepression of the properly engineered lambda xis- cIts857 prophage. In the immediately following second stage, Int causes inversion of a promoter cloned between the inverted ----P'OP phage att site and the normally oriented ----delta PO delta P' pseudo-bacterial att site. The inverted promoter can now control the expression of the studied gene and also of the lambda N gene cloned in tandem. The N product, in conjunction with the nutL site placed downstream of the promoter, permits efficient antitermination of any terminators present in the att sites, in the plasmid or in the cloned DNA, making this system efficient and of practical value. Employing the promoter-inverting plasmid, it was possible to obtain rapid onset and a high level of galactokinase synthesis from the cloned galK gene. Only a transient, 10-min induction at 42 degrees C was employed, permitting protein synthesis at 30 degrees C, which might be of importance for thermosensitive products. Furthermore, the entire promoter-inversion module can be transferred to any plasmid as a 1.3-kb AvaI-ClaI fragment (see Fig. 1).(ABSTRACT TRUNCATED AT 250 WORDS)     

Analysis of the inducible MEL1 gene of Saccharomyces carlsbergensis and its secreted product, alpha-galactosidase (melibiase)

We have determined both the nucleotide sequence of the MEL1 gene of Saccharomyces carlsbergensis and the N-terminal amino acid (aa) sequence of its extracellular gene product, alpha-galactosidase (melibiase) (alpha-Gal). The predicted translation product of MEL1 is a pre-alpha-Gal protein containing an 18 aa N-terminal signal sequence for secretion. The purified enzyme is a dimer consisting of two 50-kDal polypeptides, each of which is glycosylated with no more than eight side chains. The 5'-flank of the MEL1 gene contains a region (UASm) having certain areas of sequence homology to similar sites found upstream of the structural genes GAL1, GAL7 and GAL10, which are also regulated by the action of the products of genes GAL4 and GAL80. There are three TATA boxes between UASm and the initiation codon of pre-alpha-Gal, as well as a typical yeast cleavage/polyadenylation sequence in the 3'-flank of the gene.     

Inactivation and sedimentation of mercury from organomercurials by Klebsiella pneumoniae

Abstract A susceptibility of 63 clinical isolates of Klebsiella pneumoniae to inorganic and organic mercuric compounds was determined. 18 of them were found to be resistant to fluorescein mercuric acetate (FMA) and merbromin (MB). Moreover, all the resistant strains inactivate the antibacterial effect of FMA. The changes in the amount of organic mercury at the time of inactivation of the drug and the structures of the end products were examined in detail with the plasmid-bearing strain JK9 and its transconjugants of Escherichia coli .
The results showed that FMA was inactivated by an intracellular enzyme produced inducively and was degraded to fluorescein (sodium salt, uranine), which led to the sedimentation of metallic mercury. The discovery of the genes conferring inducible organic mercury-inactivating enzymes determined by plasmids was the next step and their application in the recovery of metallic mercury from organomercurials is now imminent.