Gene truncation

Cytochrome Cj contains a c-type haem as prosthetic group in its wedge-shaped N-terminal domain located in the inter-membrane space. This extrinsic domain is anchored to membrane by a transmembrane helix at the C-terminal end (residues 204 to 222 in bovine bc ). This helix runs alongside cytochrome b and can be removed by mild protease treatment or gene truncation to produce a protein fragment (Hase et al., 1987 Li et al., 1981). 

Fig. 156. Effects of promotor gene truncation on L7-lacZ banding pattern in mice. Cerebella were dissected free from the rest of the brain and stained in whole mount. Cerebella are viewed from posterior (POST) and anterior (ANT). Cerebella were taken from postnatal day 11 animals carrying 4 kb (top row), 500 bp (middle row) and 350 bp (bottom row) promoter constructs. The patterns are very similar to the Zebrin pattern in mouse cerebellum (compare Fig.139). Expression of L7 is absent or low in Pl-i-, P3+, P5+ (indicated with PIN in bottom panels) and P7-i- in the 500 and 350 bp constructs. In P4-i- there is a strong expression of L7 in the 500 bp construct, and a weak expression in the 350 bp construct. Reversed levels of expression are observed for the region of P4b-t- and P5a-t. In the 500 bp construct they are weakly stained (but the P4b-t and P5a + bands are visible as separate strips), in the 350 bp construct there is a strong expression of L7 over the entire area of these bands indicated with FN in lower pannel). Oberdick et al. (1993), interpretations by the authors of this chapter.

Aminetzach, T. Macpherson, J. Petrov, D. Pesticide resistance via transposon-mediated adaptive gene truncation in Drosophila. Science 2005, 309, 764-767. 

Truncated Forms. Tmncated forms of hGH have been produced, either through the actions of enzymes or by genetic methods. 2-CAP, generated by the controlled actions of the trypsin, has the first eight residues at the N-terminus of hGH removed. Other tmncated versions of hGH have been produced by modification of the gene before expression in a suitable host. The first 13 residues have been removed to yield a derivative having distinctive biological properties (30). In this latter case the polypeptide chain is not cleaved. 

On the other hand, EFN-a may also be involved in the activation of autoreactive T-cells as has been proposed for type I diabetes. An DFN-a inducible superantigen, encoded by the truncated envelope gene of a human endogenous retrovirus and specifically activating V 37 T-cells, has been detected in pancreatic lesions from type I diabetes patients, infiltrated by V 37 T-cells. Since IFN-a expression could be detected in pancreatic (3 cells in conceit with persistent viral infections, there is a clear link between viral infections and autoimmunity via IFN-a-stimulated superantigen expression. 

Misawa, N. et al.. Expression of a tomato cDNA coding for phytoene synthase in Escherichia coli, phytoene formation in vivo and in vitro, and functional analysis of the various truncated gene products, J. Biochem. (Tokyo) 116, 980, 1994. 

A naturally occurring animal model of PFK-M deficiency has been reported in English springer spaniels. Molecular analysis of this canine PFK-M deficiency disclosed that the enzyme deficiency was caused by a nonsense mutation in the penultimate exon of the PFK-M gene, leading to rapid degradation of a truncated (40 amino acid residues) and therefore unstable enzyme protein (SI8). 

A modified version of this protocol, called THIO-ITCHY, includes the random incorporation of a-phosphothioate nucleotide analogs into the parent genes [27,28]. Exonuclease III activity is inhibited at sites of analog incorporation, which relieves the efforts of producing incremental truncation aliquots. In combination with epPCR, the diversity of the fusion libraries created can be further expanded. 

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