To explore the ubiquitous impact of expression levels on molecular evolution and test the relevance of the possible underlying mechanisms, we analyzed the genome sequences of 99 strains of Escherichia coli for evolution within species in nature. These conflicts raise questions about the generalization of the E–R anticorrelation and the relevance of plausible mechanisms. However, the advent of genomic sequencing and high-throughput phenotyping, particularly for bacteria, has revealed fundamental gaps between the two evolutionary processes and has provided empirical data opposing the possible underlying mechanisms which are widely believed. However, it remains unclear whether this seemingly general law also governs recent evolution, including past and de novo, within a species. This negative correlation between expression levels and evolutionary rates (known as the E–R anticorrelation) has already been widely observed in past macroevolution between species from bacteria to animals. The evolutionary speed of a protein sequence is constrained by its expression level, with highly expressed proteins evolving relatively slowly. Only MW-induced mutant was stable after 8 generations. MW150 mutant presented 3.68 and 2.18 folds improvement in MCA and MCA/PA ratio. The best results, in terms of milk-clotting activity (MCA) and milk-clotting activity to proteolytic activity ratio (MCA/PA), were obtained with the protease secreted by the MW-induced mutant (150 s), followed by UV (10 cm*25 s), and then EMS (35 μg/mL*20 min) induced mutants.
Microwaves (MW) irradiation was done at 2450 MHz for different exposure periods (90–210 s). UV-mutagenesis was carried out at different distances (5–25 cm) from the exposure source (253 nm) for different exposure periods (5–25 s).
In this study, the fungal spore suspension was treated with different concentrations of ethyl methanesulfonate (EMS) (20–80 μg/mL) for different incubation periods (10–60 min). Enzyme biosynthesis could be improved by using random mutagenesis techniques. Rhizomucor miehei protease has been emerging as a potent substitute for the more expensive calf rennet.
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