Low copy repeats

Shaikh TH, Kurahashi H, Emanuel BS. Evolutionarily conserved low copy repeats (LCRs) in 22qll mediate deletions, duplications, translocations, and genomic instability an update and literature review. Genet Med 2001 3(1) 6 13. 

Low-copy repeat locus control region low-complexity region... 

In principle, directed evolution procedures could be repeated indefinitely until any desired activity has been attained. At some point, however, the catalyst will be sufficiently active that the host cell grows like the wild-type strain, making selection for further improvement difficult. This is true for the modified hexamer even though it is still an order of magnitude less efficient than the homodimeric MjCM [37]. Since total activity depends on the catalyst concentration as well as specific activity, reducing the available catalyst concentration can further increase selection pressure. In practice, intracellular protein concentrations can be lowered in a variety of ways, including the use of low copy plasmids [101], weak promoters [102] and inefficient ribosome binding sites [103]. 

Slides should not dry out during washing and detection, and must be handled carefully to avoid scratches. For highly repeated probes only the detection steps (steps 1-4) are necessary for the detection of low copy sequences the in situ hybridization signal can be amplified by performing steps 5-7. 

Agrobacterium-mediated transformation of plant tissue usually results in a low copy number of the DNA construct at a single insertion site. In some recombinant-DNA plant varieties reaching commercialisation T-DNAs have been found to be inserted as tandem repeats (direct or inverted instracture) at a single locus (reviewed by Smith et al., 2001). Integration of incomplete T-DNA... 

The alleles containing 4 and 9 copies of the TSER repeat were primarily confined to African populations. TSER 4 accounted for 2-7% of TSER alleles in all African populations except the Sudanese. However, TSER 4 was also found in a British Caucasian subject but not among the American-Caucasian population studied [53]. This suggests that TSER 4 occurs at a low frequency in Caucasian populations. The absence of the TSER 4 allele in the Sudanese population may be a result of the small sample size or due to the fact that this allele occurs at very low frequencies in this population. The latter possibility would make sense as this population is an admixture of Negroid and Caucasoid characteristics at both the morphological and molecular levels [17]. 

All of the oncosphere antigens cloned to date contain either one of two copies of a predicted Fnlll domain. These domains are widely distributed in eukaryotic proteins and occur also in some prokaryotic proteins (Bork and Doolittle, 1992). Approximately 2% of animal proteins include Fnlll domains. Many, but not all, of these proteins are extracellular and some have roles as adhesins. The structure of this 100 amino acid domain is highly conserved and consists of two layers with three p strands in one plane and four p strands in another (Potts and Campbell, 1996). Overall, amino acid sequence identity between different Fnlll domains is low, even between Fnlll repeat domains within fibronectin itself (Plaxco et al., 1997). Nevertheless, certain residues are highly conserved and maintain the tertiary structure of the proteins (Bork and Doolittle, 1992). Other conserved motifs such as an Arg-Gly-Asp (RGD) motif within a loop of some Fnlll domains is associated with proteins having cell adhesion properties, as discussed above (Ruoslahti and Pierschbacher, 1987 D Souza et al., 1991). 

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