Two-electron reduction of nitroaromatic compounds by Enterobacter cloacae NAD(P)H nitroreductase: description of quantitative structure-activity relationships

Enterobacter cloacae NAD(P)H:nitroreductase catalyzes the reduction of a series of nitroaromatic compounds with steady-state bimolecular rate constants (kcat/Km) ranging from 10(4) M(-1) s(-1) to 10(7) M(-1) s(-1), and oxidizing 2 moles NADH per mole mononitrocompound. Oxidation of excess NADH by polynitrobenzenes including explosives 2,4,6-trinitrotoluene (TNT) and 2,4,6-trinitrophenyl-N-methylnitramine (tetryl), has been observed as a slower secondary process, accompanied by O2 consumption. This type of 'redox cycling' was not related to reactions of nitroaromatic anion-radicals, but was caused by the autoxidation of relatively stable reaction products. The logs kcat/Km of all the compounds examined exhibited parabolic dependence on their enthalpies of single-electron- or two-electron (hydride) reduction, obtained by quantum mechanical calculations. This type of quantitative structure-activity relationships shows that the reactivity of nitroaromatics towards E. cloacae nitroreductase depends mainly on their hydride accepting properties, but not on their particular structure, and does not exclude the possibility of multistep hydride transfer.     

Protein biophysics explains why highly abundant proteins evolve slowly

The consistent observation across all kingdoms of life that highly abundant proteins evolve slowly demonstrates that cellular abundance is a key determinant of protein evolutionary rate. However, other empirical findings, such as the broad distribution of evolutionary rates, suggest that additional variables determine the rate of protein evolution. Here, we report that under the global selection against the cytotoxic effects of misfolded proteins, folding stability (ΔG), simultaneous with abundance, is a causal variable of evolutionary rate. Using both theoretical analysis and multiscale simulations, we demonstrate that the anticorrelation between the premutation ΔG and the arising mutational effect (ΔΔG), purely biophysical in origin, is a necessary requirement for abundance-evolutionary rate covariation. Additionally, we predict and demonstrate in bacteria that the strength of abundance-evolutionary rate correlation depends on the divergence time separating reference genomes. Altogether, these results highlight the intrinsic role of protein biophysics in the emerging universal patterns of molecular evolution.     

An internal AUU codon initiates a smaller peptide encoded by bacteriophage T4 baseplate gene 26

Summary Bacteriophage T4 baseplate gene 26 codes for two in-frame overlapping peptides with identical C-terminal regions. By site-directed mutagenesis we have now determined that an internal AUU, codon 114 of gene 26, is used as the initiation codon for the synthesis of a smaller peptide (gp26^*). Thus gene 26^* gives rise to a peptide of 95 amino acid residues with an M_r of 10873, while the complete gene 26 encodes a peptide of 208 amino acid residues of M_r 23 880. Expression of gene 26^* is shown to depend on the RNA secondary structure in the translational initiation region of this gene.     

Transmission of amber mutants of bacteriophage T4. III. Thermostability of the replication of amber mutants in cells of a non-permissive host is typical for the majority of phage tail genes

The article deals with determination of the spreading of the earlier discovered phenomenon of the temperature sensitivity of multiplication of T4 phage amber mutants. On the basis of the study of the dependence of multiplication of 50 amber mutants in 22 genes of T4 phage tail in the cells of non-permissive host on the incubation temperature in the range of 15-41 degrees C, the following conclusion is drawn: temperature sensitivity of multiplication of amber mutants appears to be gene-specific and is widely spread among T4 phage genes, i.e. in the case of amber mutants the burst size decreases, even for 14 tail genes, by several orders with the increase in incubation temperature. Temperature sensitivity of multiplication is typical of amber mutants in the genes whose proteins are either of small number in a phage particle (several molecules) or play the role of catalytic factors. Moreover, genes, amber mutants of which possess temperature sensitivity of multiplication, map in defined clusters.     

Transmission of amber mutants of bacteriophage T4. IV. The frequency of the phenomenon of temperature sensitivity of replication in non-permissive cells of amber mutants for the head genes

Dependence of multiplication of 42 single and double amber mutants in 16 phage head genes on the incubation temperature was studied in the cells of non-permissive host. For amber mutants in 6 head genes the birst size decreases by several orders, with the increase of the incubation temperature. Among amber mutants of the above mentioned genes, mutants in genes 4 and 65 can be distinguished as those with considerably large burst size at low temperature. Phage head genes form the groups, according to temperature sensitivity of multiplication of amber mutants. These groups, together with corresponding groups of phage tail genes, constitute common temperature-sensitive and non-sensitive gene groups on the phage genomic map.     

Nucleotide sequence of gene 31 of the T4 bacteriophage

We have determined the nucleotide sequence of a region of 656 nucleotides comprising the 31 gene of bacteriophage T4. The coding region consisted of 333 nucleotides directing the synthesis of a polypeptide of 111 amino acids, with a calculated molecular weight of 12,060. The upstream sequence contains the consensus sequences for T4 early and two middle promoters. The downstream sequence contains the consensus sequence for T4 late promoter and the inverted repeats. In addition, there are two incomplete open reading frames in the sequenced region.