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)

Rare AGA or AGG codons close to the initiation codon inhibit protein synthesis by a tRNA-sequestering mechanism as toxic minigenes do. To further understand this mechanism, a parallel analysis of protein synthesis and peptidyl-tRNA accumulation was performed using both a set of lacZ constructs where AGAAGA codons were moved codon by codon from +2, +3 up to +7, +8 positions and a series of 3-8 codon minigenes containing AGAAGA codons before the stop codon. Beta-galactosidase synthesis from the AGAAGA lacZ constructs (in a Pth defective in vitro system without exogenous tRNA) diminished as the AGAAGA codons were closer to AUG codon. Likewise, beta-galactosidase expression from the reporter +7 AGA lacZ gene (plus tRNA, 0.25 microg/microl) waned as the AGAAGAUAA minigene shortened. Pth counteracted both the length-dependent minigene effect on the expression of beta-galactosidase from the +7 AGA lacZ reporter gene and the positional effect from the AGAAGA lacZ constructs. The +2, +3 AGAAGA lacZ construct and the shortest +2, +3 AGAAGAUAA minigene accumulated the highest percentage of peptidyl-tRNA(Arg4). These observations lead us to propose that hungry codons at early positions, albeit with less strength, inhibit protein synthesis by a minigene-like mechanism involving accumulation of peptidyl-tRNA.
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PMID:Minigene-like inhibition of protein synthesis mediated by hungry codons near the start codon. 1858 64

The expression of reporter gene may be induced by activation of cryptic signalling sequences, as we found while constructing the mutS-lacZ fusion gene. We cloned the Escherichia coli lacZ gene encoding beta-galactosidase into a plasmid vector carrying the Thermus thermophilus mutS gene. The clones expected to produce beta-galactosidase as the C-terminal fusion were selected for the complementation of beta-galactosidase activity in a lacZ deficient E. coli strain. Surprisingly, one of the clones, though displaying beta-galactosidase activity, did not produce the fusion protein. As shown by DNA sequencing a 92 bp fragment in the 3' part of mutS gene was substituted by a 19 bp sequence. As the consequence of the resultant frameshift, a truncated MutS peptide was translated instead of beta-galactosidase fusion. The cloned lacZ gene lacked its ribosome binding site, so lacZ expression could be explained by activation of a cryptic ribosome binding site in the 3' end of mutS gene. This observation shows that fusion domains in reporter systems are possible to produce accidentally misleading signals. This observation also suggests that some triplets like AGG and AGA, present in the canonical ribosome binding sequence, are rarely used codons to prevent chaotic protein translation.
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PMID:A cryptic ribosome binding site, false signals in reporter systems and avoidance of protein translation chaos. 1960 65


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