Mutation domain

If Fas gene mutations are significant in tumor biology, mutations may be clustered in the most important region of the gene. Accordingly, the hot spot of the mutations in cancers and the relationship between the mutation domain and the functional impairment are discussed in this section. 

Observations that the 5 end of the mutation domain is near the transcriptional promoter stimulated speculation that the initiation of transcription is in some way involved in the generation of mutations. Betz et al. (1994) showed that the two transcriptional enhancer elements in the K locus, one in the JC intron and the other 9 kb 3 to CK, are important for effective hypermutation. The intron enhancer appeared to be absolutely required, whereas deletion of the 3 enhancer reduced but did not abolish mutation. The promoter 5 of the VK transcription start site (Falkner and Zachau, 1984 Parslow et al., 1984) was replaced by the human P-globin promoter without deleterious effect on mutation, indicating that specific promoter elements may not be required. Heavy chain transgenes with a heterologous promoter can also undergo mutation (Tumas-Brundage and Manser, 1997). 

The importance of the position of the promoter was also demonstrated by Tumas-Brundage and Manser (1997) moving the VH promoter 750 bp 5 to its normal location resulted in a 5 shift in the mutation domain. However, as Scharff et al. (1997) have pointed out, it is not yet clear whether it is transcription itself that is critical or some process dependent on or related to transcription, such as enhanced accessibility of the DNA in the transcribed gene segment. Moreover, antibodies produced in response to antigens that do not require collaboration of B and T cells... 

PREDICTED LOCALISATION OF THE MUTATED DOMAINS (hatcfwd) ON A STRUCTURAL MOOEL OF PLANT NTTRATE REDUCTASE MONOMER (gray protein or mRNA aboont) " A f AO J MoCo g t— v 1 7 FAD J 1 ... 

Fig. 2. Biochemical classification of the nia mutants, mutated domains and intragenic complementation. A collection of Nicotiana plumbaginifolia nia mutants (defective for NR apoenzyme) was tested for NR protein and activities (Cherel et al., 1990) and checked for in vivo and in vitro intragenic complementation (Pelsy Gonneau, 1991). NR protein amounts were measured by a sandwich ELISA test using as first antibody the anti-corn NR monoclonal antibody 96.9.25 (Ch6rel eta/., 1985) shown to be directed against the haem domain (M. Kavanagh, personal communication Meyer etal., 1991). The result is shown here as + or when a positive or negative ELISA test, respectively, was observed. Many class 4 mutants, most probably frameshift and deletion mutants, complement class 3 but not class 2 mutants.

Fig. 7. Adsorption isotherms for mutated cellulose binding domains (reproduced from [13]). This graph illustrates the importance of tyrosine residues for cellulose binding in the cellulose binding domain. NMR comparisons between the native binding domain and the mutated domains were given in [13]. Note that Y32 A, which shows no affinity for crystalline cellulose, showed very slight chemical shifts in structure from the wild type as measured by NMR...

Src tyrosine kinase contains both an SH2 and an SH3 domain linked to a tyrosine kinase unit with a structure similar to other protein kinases. The phosphorylated form of the kinase is inactivated by binding of a phosphoty-rosine in the C-terminal tail to its own SH2 domain. In addition the linker region between the SH2 domain and the kinase is bound in a polyproline II conformation to the SH3 domain. These interactions lock regions of the active site into a nonproductive conformation. Dephosphorylation or mutation of the C-terminal tyrosine abolishes this autoinactivation. 

T4 lysozyme has two such cavities in the hydrophobic core of its a helical domain. From a careful analysis of the side chains that form the walls of the cavities and from building models of different possible mutations, it was found that the best mutations to make would be Leu 133-Phe for one cavity and Ala 129-Val for the other. These specific mutants were chosen because the new side chains were hydrophobic and large enough to fill the cavities without making too close contacts with surrounding atoms. 

How do the mutations identified by phage display improve binding specificity There is as yet no direct stmctural information on the phage-selected inhibitors however they can be modeled using data from the crystal structures of other Kunitz domains bound to serine proteinases. These studies lead to the conclusion that the mutations identified by phage display improve binding specificity by maximizing complementarity between the... 

POU regions bind to DNA by two tandemly oriented helix-turn-helix motifs Much remains to be learnt about the function of homeodomains in vivo Understanding tumorigenic mutations The monomeric p53 polypeptide chain is divided in three domains The oligomerization domain forms tetramers The DNA-binding domain of p53 is an antiparallel P barrel... 

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