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

The gene for initiation factor IF2, infB, represents one of the few examples in Escherichia coli of genes encoding two protein products in vivo. In a previous work, our group showed that both forms of IF2 (alpha and beta) are closely related and may arise from two independent translational events on infB mRNA. Unambiguous mapping and rigorous determination of the nature of the initiation triplet for IF2 beta, the smaller form of IF2, is critical for future mutagenesis of this codon, required for investigating the biological importance of both IF2 alpha and IF2 beta. Three types of experiments were carried out. First, a 77-bp deletion was created at the beginning of the structural gene leading to premature termination of IF2 alpha synthesis. Under these conditions, IF2 beta is still formed. Second, various Bal31 digests of infB containing the 77-bp deletion were fused to lacZ. Any synthesis of a fused protein with beta-galactosidase activity should reflect the occurrence of an initiation event on the messenger corresponding to this DNA segment. It was consequently possible to locate the IF2 beta initiation site within an 18-base region containing an in-phase GUG codon. Third, to avoid any artefactual reinitiation event possibly occurring under our experimental conditions, we fused to lacZ an infB fragment devoid of IF2 alpha start sequences but containing genetic information for this 18-base region. A hybrid protein with beta-galactosidase activity was synthesized. Moreover, its NH2-terminal amino acid sequence coincided with that of IF2 beta, demonstrating that GUG, located 471 bases downstream from the IF2 alpha external start codon, is the internal start codon for the shorter form of IF2.
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PMID:Characterization of the translational start site for IF2 beta, a short form of Escherichia coli initiation factor IF2. 211 58

Protein and operon fusions between lacZ and various genes of the nusA,infB operon have been constructed on lambda bacteriophages and used to show that the operon is negatively regulated by the level of NusA protein. Overproducing NusA (but not IF2) from a multicopy plasmid reduces the level of beta-galactosidase from the fusions indicating repression of the operon. Introducing the lambda carrying the fusions into nusA mutant strains produces a higher level of beta-galactosidase-indicative of derepression of the operon. In particular, a larger form of the NusA protein which does not affect bacterial growth per se causes a derepression of the operon. As both protein and operon fusions respond equivalently, we conclude that the nusA protein is acting at the transcriptional level to regulate expression of the nusA, infB operon.
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PMID:Effect of NusA protein on expression of the nusA,infB operon in E. coli. 298 84

The Escherichia coli gene secY (pr1A) codes for an integral membrane protein that plays an essential role in protein export. We previously isolated cold-sensitive mutations (ssy) as extragenic suppressors of temperature-sensitive secY24 mutation. Now we show that the ssyG class of mutations are within infB coding for the translation initiation factor IF2. The mutants produce altered forms of IF2 with a cold-sensitive in vitro activity to form a translation initiation complex. The mutation suppresses not only secY24 but also other secretion-defective mutations such as secA51 and rp10215. The beta-galactosidase enzyme activity of the MalE-LacZ 72-47 hybrid protein is strikingly reduced in the ssyG mutant at the permissive high temperature, while the hybrid protein itself is normally synthesized. This effect, which was observed only for the hybrid protein with a functional signal sequence, may result from some alteration in the cellular localization of the protein. These results suggest that IF2 or the translation initiation step can modulate protein export reactions. The isolation of cold-sensitive ssyG mutations in infB provides genetic evidence that IF2 is indeed essential for normal growth of E. coli cells.
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PMID:Altered translation initiation factor 2 in the cold-sensitive ssyG mutant affects protein export in Escherichia coli. 353 91

The gene infB codes for the two forms of translational initiation factor IF2: IF2 alpha (97 300 daltons) and IF2 beta (79 700 daltons). To determine whether the two forms differ at their N terminus, purified IF2 alpha and IF2 beta were subjected to 11 or more steps of Edman degradation. The N-terminal amino acid sequences are completely different, but match perfectly the DNA sequences at the beginning of the infB open reading frame and an in-phase region 471 bp downstream. A fusion was constructed between the proximal half of the infB gene and the lacZ gene lacking the region coding for the first eight amino acids. The fused gene expresses two products of 170 000 and 150 000 daltons, corresponding to the fused proteins IF2 alpha-beta-galactosidase and IF2 beta-beta-galactosidase, which confirms in vivo that the IF2 forms differ at their N terminus. A deletion of the 5'-non-translated region of the fused gene, including the Shine/Dalgarno ribosomal binding site, results in the expression of IF2 beta-beta-galactosidase but not IF2 alpha-beta-galactosidase. This strongly suggests that IF2 beta results from independent translation rather than from a precise proteolytic cleavage of IF2 alpha. Further evidence for initiation of protein synthesis at the putative IF2 alpha and IF2 beta start sites was sought by using an in vitro dipeptide synthesis assay. A DNA fragment containing the entire infB gene was cloned into three plasmid vectors and the resulting recombinant DNAs were used as templates in assays containing fMet-tRNA and various labelled aminoacyl-tRNAs.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Two translational initiation sites in the infB gene are used to express initiation factor IF2 alpha and IF2 beta in Escherichia coli. 389 4

The carboxy-terminal region of translational initiation factor IF2 is a common region to the three active forms of the factor (alpha, beta and gamma) but its function is still unknown. We report here that this region of IF2 carries at least one domain which is homologous to the N-terminal and middle part of the cI repressor of lambda phage. The IF2 homologous domain harbors functionally important features of the lambda repressor, e.g. the helix-turn-helix motif and some of the residues essential for the structure of the hydrophobic core of the repressor. This homologous domain of IF2 was fused to the beta-galactosidase protein. The hybrid protein, as well as IF2 itself, shows a consistent DNA binding activity in nitrocellulose filtration assays but does not display the specificity of the cI repressor for the PR operator. The implication of this domain in the transcriptional activity of IF2, reported by others, is discussed.
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PMID:Domain of E. coli translational initiation factor IF2 homologous to lambda cI repressor and displaying DNA binding activity. 847 56