Protein expression refers to the techniques in which a protein of interest is synthesized, modified or regulated in cells. The blueprints for proteins are stored in DNA which is then transcribed to produce messenger RNA (mRNA). mRNA is then translated into protein. In prokaryotes, this process of mRNA translation occurs simultaneously with mRNA transcription. In eukaryotes, these two processes occur at separate times and in separate cellular regions (transcription in nucleus and translation in the cytoplasm). Recombinant protein expression utilizes cellular machinery to generate proteins, instead of chemical synthesis of proteins as it is very complex. Proteins produced from such DNA templates are called recombinant proteins and DNA templates are simple to construct. Recombinant protein expression involves transfecting cells with a DNA vector that contains the template. The cultured cells can then transcribe and translate the desired protein. The cells can be lysed to extract the expressed protein for subsequent purification. Both prokaryotic and eukaryotic protein expression systems are widely used. The selection of the system depends on the type of protein, the requirements for functional activity and the desired yield. These expression systems include mammalian, insect, yeast, bacterial, algal and cell-free. Each of these has pros and cons. Mammalian expression systems can be used for transient or stable expression, with ultra high-yield protein expression. However, high yields are only possible in suspension cultures and more demanding culture conditions. Insect cultures are the same as mammalian, except that they can be used as both static and suspension cultures. These cultures also have demanding culture conditions and may also be time-consuming. Yeast cultures can produce eukaryotic proteins and are scalable, with minimum culture requirements. Yeast cultures may require growth culture optimization. Bacterial cultures are simple, scalable and low cost, but these may require protein-specific optimization and are not suitable for all mammalian proteins. Algal cultures are optimized for robust selection and expression, but these are less developed than other host platforms. Cell-free systems are open, free of any unnatural compounds, fast and simple. This system is, however, not optimal for scaling up.
Protein expression refers to the techniques in which a protein of interest is synthesized, modified or regulated in cells. The blueprints for proteins are stored in DNA which is then transcribed to produce messenger RNA (mRNA). mRNA is then translated into protein. In prokaryotes, this process of mRNA translation occurs simultaneously with mRNA transcription. In eukaryotes, these two processes occur at separate times and in separate cellular regions (transcription in nucleus and translation in the cytoplasm). Recombinant protein expression utilizes cellular machinery to generate proteins, instead of chemical synthesis of proteins as it is very complex. Proteins produced from such DNA templates are called recombinant proteins and DNA templates are simple to construct. Recombinant protein expression involves transfecting cells with a DNA vector that contains the template. The cultured cells can then transcribe and translate the desired protein. The cells can be lysed to extract the expressed protein for subsequent purification. Both prokaryotic and eukaryotic protein expression systems are widely used. The selection of the system depends on the type of protein, the requirements for functional activity and the desired yield. These expression systems include mammalian, insect, yeast, bacterial, algal and cell-free. Each of these has pros and cons. Mammalian expression systems can be used for transient or stable expression, with ultra high-yield protein expression. However, high yields are only possible in suspension cultures and more demanding culture conditions. Insect cultures are the same as mammalian, except that they can be used as both static and suspension cultures. These cultures also have demanding culture conditions and may also be time-consuming. Yeast cultures can produce eukaryotic proteins and are scalable, with minimum culture requirements. Yeast cultures may require growth culture optimization. Bacterial cultures are simple, scalable and low cost, but these may require protein-specific optimization and are not suitable for all mammalian proteins. Algal cultures are optimized for robust selection and expression, but these are less developed than other host platforms. Cell-free systems are open, free of any unnatural compounds, fast and simple. This system is, however, not optimal for scaling up.
The formation of DNA from an RNA template using reverse transcription leads to the formation of double-stranded complementary DNA or cDNA. The challenges with this process include 1. Maintaining the integrity of RNA, 2. Hairpin loops or other secondary structures formed by single-stranded RNA can also affect cDNA synthesis, and 3. DNA-RNA hybrids, which may result when the first strand of cDNA is formed. For the first challenge, using workflows that involve proper isolation and storage of RNA, and maintaining a nuclease-free environment helps obtain RNA with ideal 260/230 ratios. Using a reverse transcriptase that can tolerate high temperatures (50-55oC), overcomes obstacles imposed by secondary RNA structures. Finally, RNase H has the ability to hydrolyze RNA before the formation of a second cDNA strand. It is important to ensure that RNase H activity is optimal because higher RNase H activity leads to premature degradation of the RNA template. Many reverse transcriptases offer built-in RNase H activity.
The formation of DNA from an RNA template using reverse transcription leads to the formation of double-stranded complementary DNA or cDNA. The challenges with this process include 1. Maintaining the integrity of RNA, 2. Hairpin loops or other secondary structures formed by single-stranded RNA can also affect cDNA synthesis, and 3. DNA-RNA hybrids, which may result when the first strand of cDNA is formed. For the first challenge, using workflows that involve proper isolation and storage of RNA, and maintaining a nuclease-free environment helps obtain RNA with ideal 260/230 ratios. Using a reverse transcriptase that can tolerate high temperatures (50-55oC), overcomes obstacles imposed by secondary RNA structures. Finally, RNase H has the ability to hydrolyze RNA before the formation of a second cDNA strand. It is important to ensure that RNase H activity is optimal because higher RNase H activity leads to premature degradation of the RNA template. Many reverse transcriptases offer built-in RNase H activity.
The formation of DNA from an RNA template using reverse transcription leads to the formation of double-stranded complementary DNA or cDNA. The challenges with this process include 1. Maintaining the integrity of RNA, 2. Hairpin loops or other secondary structures formed by single-stranded RNA can also affect cDNA synthesis, and 3. DNA-RNA hybrids, which may result when the first strand of cDNA is formed. For the first challenge, using workflows that involve proper isolation and storage of RNA, and maintaining a nuclease-free environment helps obtain RNA with ideal 260/230 ratios. Using a reverse transcriptase that can tolerate high temperatures (50-55oC), overcomes obstacles imposed by secondary RNA structures. Finally, RNase H has the ability to hydrolyze RNA before the formation of a second cDNA strand. It is important to ensure that RNase H activity is optimal because higher RNase H activity leads to premature degradation of the RNA template. Many reverse transcriptases offer built-in RNase H activity.
Generally isolating RNA from Gram-negative bacteria is easy, however keeping your working environment clean and RNase free (use RNase inhibitor) is essential. Some common points to keep in mind: a) Use fresh samples for isolation or store them by freezing in RNA stabilizing buffer until use. b) Choose the bacterial input amounts carefully, to ensure buffer volumes are adequate and not to overload the columns.
Generally isolating RNA from Gram-negative bacteria is easy, however keeping your working environment clean and RNase free (use RNase inhibitor) is essential. Some common points to keep in mind: a) Use fresh samples for isolation or store them by freezing in RNA stabilizing buffer until use. b) Choose the bacterial input amounts carefully, to ensure buffer volumes are adequate and not to overload the columns.
When extracting nucleic acids from cell cultures, thorough homogenization of cells via vortexing in lysis buffer is very necessary. Choose the best RNA isolation method keeping in mind the downstream applications, generally, column-based isolations result in clean and concentrated RNA samples. Downstream applications like sequencing and cDNA synthesis require high-quality RNA, always treat the samples with DNases and check their integrity by running a gel.
Generally isolating RNA from Gram-negative bacteria is easy, however keeping your working environment clean and RNase free (use RNase inhibitor) is essential. Some common points to keep in mind: a) Use fresh samples for isolation or store them by freezing in RNA stabilizing buffer until use. b) Choose the bacterial input amounts carefully, to ensure buffer volumes are adequate and not to overload the columns.
Generally isolating RNA from Gram-negative bacteria is easy, however keeping your working environment clean and RNase free (use RNase inhibitor) is essential. Some common points to keep in mind: a) Use fresh samples for isolation or store them by freezing in RNA stabilizing buffer until use. b) Choose the bacterial input amounts carefully, to ensure buffer volumes are adequate and not to overload the columns.
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