Recombinant Passenger Proteins Can Be Conveniently Purified by One-Step Affinity Chromatography.

Fusion tag is one of the best available tools to date for enhancement of the solubility or improvement of the expression level of recombinant proteins in Escherichia coli. Typically, two consecutive affinity purification steps are often necessitated for the purification of passenger proteins. As a fusion tag, acyl carrier protein (ACP) could greatly increase the soluble expression level of Glucokinase (GlcK), α-Amylase (Amy) and GFP. When fusion protein ACP-G2-GlcK-Histag and ACP-G2-Amy-Histag, in which a protease TEV recognition site was inserted between the fusion tag and passenger protein, were coexpressed with protease TEV respectively in E. coli, the efficient intracellular processing of fusion proteins was achieved. The resulting passenger protein GlcK-Histag and Amy-Histag accumulated predominantly in a soluble form, and could be conveniently purified by one-step Ni-chelating chromatography. However, the fusion protein ACP-GFP-Histag was processed incompletely by the protease TEV coexpressed in vivo, and a large portion of the resulting target protein GFP-Histag aggregated in insoluble form, indicating that the intracellular processing may affect the solubility of cleaved passenger protein. In this context, the soluble fusion protein ACP-GFP-Histag, contained in the supernatant of E. coli cell lysate, was directly subjected to cleavage in vitro by mixing it with the clarified cell lysate of E. coli overexpressing protease TEV. Consequently, the resulting target protein GFP-Histag could accumulate predominantly in a soluble form, and be purified conveniently by one-step Ni-chelating chromatography. The approaches presented here greatly simplify the purification process of passenger proteins, and eliminate the use of large amounts of pure site-specific proteases.

A cost-effective high-resolution melting approach using the EvaGreen dye for DNA polymorphism detection and genotyping in plants.

High-resolution melting (HRM) analysis relies on the use of fluorescent dyes, such as LCGreen, ResoLight, and SYTO9, which bind in a saturated manner to the double-stranded DNAs. These dyes are expensive in use and may not be affordable when dealing with a large quantity of samples. EvaGreen is a much cheaper DNA helix intercalating dye and has been used in quantitative real-time polymerase chain reaction (PCR) and post-PCR DNA melt curve analysis. Here we report on the development of an EvaGreen-based HRM analysis and its performance, in comparison with the popular LCGreen-based HRM analysis, in detection of DNA polymorphism in plants. We found that various polymorphisms ranged from single nucleotide polymorphisms (SNPs) to Indels were equally detected by using EvaGreen- or LCGreen-based HRM. EvaGreen dye was sensitive enough in discovery of SNPs in fivefold pooled samples. Using this economical dye we successfully identified multiple novel mutant alleles of Gln1-3 gene, which produces a cytosolic glutamine synthetase isoenzyme (GS1), in a maize ethyl methanesulfonate (EMS)-mutagenized library, and genotyped rice mapping populations with SNP markers. The current results suggest that EvaGreen is a promising dye for HRM analysis for its ease to use and cost effectiveness.