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The observation that mutations in the Escherichia coli genes umuC+ and umuD+ abolish mutagenesis induced by UV light strongly supported the counterintuitive notion that such mutagenesis is an active rather than passive process. Genetic and biochemical studies have revealed that umuC+ and its homolog dinB+ encode novel DNA polymerases with the ability to(More)
Transfer of alanine from Escherichia coli alanyl-tRNA synthetase (AlaRS) to RNA minihelices that mimic the amino acid acceptor stem of tRNA(Ala) has been shown, by analysis of variant minihelix aminoacylation activities, to involve a transition state sensitive to changes in the 'discriminator' base at position 73. Solution NMR has indicated that this(More)
Aminoacyl-tRNA synthetases are responsible for activating specific amino acids and transferring them onto cognate tRNA molecules. Due to the similarity in many amino acid side chains, certain synthetases misactivate non-cognate amino acids to an extent that would be detrimental to protein synthesis if left uncorrected. To ensure accurate translation of the(More)
DNA polymerase III (DNA pol III) efficiently replicates the Escherichia coli genome, but it cannot bypass DNA damage. Instead, translesion synthesis (TLS) DNA polymerases are employed to replicate past damaged DNA; however, the exchange of replicative for TLS polymerases is not understood. The umuD gene products, which are up-regulated during the SOS(More)
The cellular response to DNA damage in Escherichia coli is controlled in part by the activity of the umuD gene products. The full-length dimeric UmuD(2) is the initial product that is expressed shortly after the induction of the SOS response and inhibits bacterial mutagenesis, allowing for error-free repair to occur. Over time, the slow auto-cleavage of(More)
The homodimeric umuD gene products play key roles in regulating the cellular response to DNA damage in Escherichia coli. UmuD(2) is composed of 139-amino acid subunits and is up-regulated as part of the SOS response. Subsequently, damage-induced RecA·ssDNA nucleoprotein filaments mediate the slow self-cleavage of the N-terminal 24-amino acid arms yielding(More)
DNA polymerases of the Y family promote survival by their ability to synthesize past lesions in the DNA template. One Escherichia coli member of this family, DNA pol V (UmuC), which is primarily responsible for UV-induced and chemically induced mutagenesis, possesses a canonical beta processivity clamp-binding motif. A detailed analysis of this motif in DNA(More)
The aminoacyl-tRNA synthetases are an ancient group of enzymes that catalyze the covalent attachment of an amino acid to its cognate transfer RNA. The question of specificity, that is, how each synthetase selects the correct individual or isoacceptor set of tRNAs for each amino acid, has been referred to as the second genetic code. A wealth of structural,(More)
Members of the Y family of DNA polymerases are specialized to replicate lesion-containing DNA. However, they lack 3'-5' exonuclease activity and have reduced fidelity compared to replicative polymerases when copying undamaged templates, and thus are potentially mutagenic. Y family polymerases must be tightly regulated to prevent aberrant mutations on(More)
Editing reactions catalyzed by aminoacyl-tRNA synthetases are critical for accurate translation of the genetic code. To date, this activity, whereby misactivated amino acids are hydrolyzed either before or after transfer to noncognate tRNAs, has been characterized extensively only in the case of class I synthetases. Class II synthetases have an active-site(More)