Point mutations, production

Small-scale mutations include point mutations, which are single nucleotide substitutions, and small deletion and insertion mutations. Point mutations can be further classified into (1) missense mutations, which lead to amino acid change and result in production of abnormal protein, (2) silent mutations, which do not lead to a change in amino acid, and (3) nonsense mutations, in which substitution of a single nucleotide results in formation of a stop codon and a truncated protein. Deletion and insertion mutations result in deletion or insertion of a number of nucleotides that is divisible by 3. This leads to a change in the number of amino acids and a shorter or longer protein, or to an insertion or deletion of a number of nucleotides that is not divisible by 3. This... 

Fur has a regulatory influence on the acid-shock response in E. coli and Salmonella. The acid-response reactions are important for the cells to survive when they pass the acidic gut. In Salmonella, a Fur-dependent, but iron-independent, regulation of acid-response genes is observed. Certain point mutations of Fur (e.g. H90R) do not respond to iron, but are able to regulate an acid-response gene (Foster, 2000). Unfortunately, the functions of the Fur-dependent gene products in acid response are not known. 

Zoller, M. J., and Smith, M., Oligonucleotide-Directed Mutagenesis Using M13-Derived Vectors an Efficient and General Procedure for the Production of Point Mutations in Any Fragment of DNA. Nucleic Acids Res., 1982. 10(20) pp. 6487-6500. 

Some investigators described artifactual DNA sequence alterations after formalin fixation, when testing DNA samples extracted from FFPE tissues. Williams et al.46 reported that up to one mutation artifact per 500 bases was found in FFPE tissue. They also found that the chance of artificial mutations in FFPE tissue sample was inversely correlated with the number of cells used for DNA extraction that is, the fewer cells, the more the artifacts. However, they mentioned that these artifacts can be distinguished from true mutations by confirmational sequencing of independent amplification products, in essence comparing the product of different batches. Quach et al.47 documented that damaged bases can be found in DNA extracted from FFPE tissues, but are still readable after in vitro translesion synthesis by Taq DNA polymerase. They pointed out that appropriate caution should be exercised when analyzing small numbers of templates or cloned PCR products derived from FFPE tissue samples. 

Point mutations resulting in amino acid substitutions in PrP or, in two cases, production of a stop codon resulting in expression of a truncated PrP ... 

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