Sequence-variable mosaics

Wei W, Davis RE, Jomantiene R, Zhao Y. Ancient, recurrent phage attacks and recombinations shaped dynamic sequence-variable mosaics at the root of phytoplasma genome evolution. Proc Natl Acad Sci USA. 2008 105 11827-32. 

Ribosomal RNA molecules are mosaics, that is, certain rRNA sequences are highly conserved among species, although others are variable. 

The cytoplasmic domains of all of these receptors have an intrinsic protein tyrosine kinase activity, and all the receptors have hydrophobic transmembrane sequences. Their extracellular regions are more variable in stmcture. Depending on the receptor, they may contain a range of domains, including (1) immrmoglobulin domains, (2) cysteine-rich motifs, (3) fibronectin type III repeats, and (4) EGF motifs. These can be present singly or in different combinations. Growth factor receptors are therefore examples of mosaic proteins. 

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