Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.2.1.23 (beta-galactosidase)
 14,648 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The chvB operon of Agrobacterium tumefaciens is required for bacterial attachment to plant cells and for efficient crown gall tumor formation. As defined by the virulence phenotypes of mutants with transposon insertions mapping in the region, the operon was previously mapped to a 5-kilobase (kb) stretch of chromosomal DNA. We report here that the operon is actually about 8.5 kb long and that it contains a 7-kb gene coding for a large membrane protein involved in the synthesis of cyclic beta-1,2-glucan. Mutants with transposon insertions within the 5-kb phenotypically defined operon do not synthesize this functional protein, do not synthesize beta-1,2-glucan, and do not form tumors. However, mutants with insertions that map up to 3.5 kb downstream of the phenotypically defined operon synthesize truncated proteins that are active in beta-1,2-glucan synthesis. These mutants form tumors. The truncated proteins correspond closely in size with the map positions of the insertions, suggesting that the insertions truncate the proteins by translational termination. A plasmid that contains only the phenotypically defined chvB operon also codes for a truncated protein. A fusion product between the protein and beta-galactosidase carried on a Tn3-HoHo1 insertion was observed in one mutant. Partial trypsin digestion of wild-type inner membranes generated truncated proteins that were active in beta-1,2-glucan synthesis, demonstrating that a large portion of the protein is not required for beta-1,2-glucan synthesis. The correlation between beta-1,2-glucan synthesis by the truncated proteins and tumorigenesis strongly implicates the polysaccharide product of this protein in tumor formation.
 ...
PMID:Identification of the product of an Agrobacterium tumefaciens chromosomal virulence gene. 285 22

Several lacZ chimeric genes were constructed by fusing the truncated lacZ sequence of Escherichia coli to N-terminal sequences of few other genes. Promoters used to direct expression of the chimeric genes were the promoter for 35S RNA of cauliflower mosaic virus (P35S) as well as those of the small subunit gene of ribulose bisphosphate carboxylase and the octopine synthase gene. These constructs were introduced into tobacco cells using a Ti plasmid of Agrobacterium tumefaciens, and beta-galactosidase activity in uncloned and cloned calli derived from the crown galls were examined. The results showed that the P35S-linked lacZ chimeric gene is expressed very efficiently. When slices of the crown gall carrying this chimeric gene were placed on plates containing indicator XGal, localized areas of the outgrowth turned deep blue, whereas no such areas were found in the crown gall having promoter-less lacZ. Calli from galls containing this construct expressed beta-galactosidase activity at an eight-fold higher level (approx. 7000 units/mg protein) than the endogenous activity (approx. 900 units/mg protein). Some of the calli displayed over 20-fold higher activity. Actively growing mini calli expressing activity higher than 4000 units/mg protein dyed deep blue on XGal agar medium such that they were distinguishable from calli having no lacZ. Half of the uncloned P35S-lacZ transformant calli showed activity higher than this level. These results indicate that the lacZ gene linked to a strong promoter such as P35S is useful as a biochemical and histochemical marker gene in plant cells.
 ...
PMID:Escherichia coli lacZ gene as a biochemical and histochemical marker in plant cells. 313 64