Mosaic genes

Zumft, W. G., and Komer, H. (1997). Enzyme diversity and mosaic gene organization in denitrification. Antonie Leeuwenhoek. 71, 43-58. 

Each gene can contain one to several intron insertions. Each of these is 10-10,000 nucleotide pairs. The moderately repetitive DNA sequences of introns could create hot spots for recombination to rearrange exonic sequences. For recombination to create such mosaic genes, the intron must contain five-ten times more DNA than the exon (Gilbert, 1978). The bands of polytene chromosomes contain sufficient amounts of DNA for this to occur. Thus, this observation is in good agreement with the one structural gene — one band hypothesis. 

Hakenbeck, R. BahneUe, N. Weber, B. Gardes, C. Keck, W. de Saizieu, A. Mosaic Genes and Mosaic Chromosomes Intra- and Interspecies Genomic Variation oiStreptococcus Pneumoniae. Infect. Immun. 2001, 69, 2477-2486. 

A second mechanism of resistance involves alterations in PBPs which affect binding of /3-lactams. These changes have been found to occur by multiple substitutions through recombination rather than point mutations. Acquired penicillin resistance in Strep, pneumoniae is because of such gene mosaics which code for an altered yet functional PBP with reduced affinity for penicillin. Sections of the susceptible PBP gene have been replaced by other DNA sequences, presumably via transformation. 

Mintz, B and Bradl, M. (1991). Mosaic expression of a tyrosinase fusion gene in albino mice yields a heritable striped coat color pattern in transgenic homozygotes. Proc. Natl. Acad. Sci. USASS 9643-9647. 

Porter, S. )., and Meyer, C. J. (1994). A distal tyrosinase upstream element stimulates gene expression in neural-crest-derived melanocytes of transgenic mice position-independent and mosaic expression. Development 120 2103-2111. 

Hendy, G. N., Minutti, C., Canaff, L., et al. (2003) Recurrent familial hypocalcemia due to germline mosaicism for an activating mutation of the calcium-sensing receptor gene. J. Clin. Endocrinol. Metab. 88, 3674-3681. 

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