Molecular parahomology

Molecular parahomology - Molecular parahomology The concept...

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Molecular parahomology The concept of parahomology applies equally to both the macroscopic structures of organisms and structures on the molecular level. Confirmation: On the molecular level, the existence of parahomology is quite impressive. Many proteins of very different function have strikingly similar amino acid sequences and three-dimensional structures. A frequently cited example is lysozyme and α-lactalbumin. Almost all animals have lysozyme. It is a secreted protein used to degrade bacterial cell walls as a means of defense (Voet and Voet 1995 , p. 381). α-Lactalbumin is very similar structurally to lysozyme, even though its function is very different (it is involved in mammalian lactose synthesis in the mammary gland) (Acharya et al . 1989 ; Voet and Voet 1995 , p. 608). It can often be inferred from molecular phylogenies, as it has been here, that the protein with the more basic function (e.g. lysozyme) is also the older protein (Prager and Wilson 1988 ; Qasba and Kumar 1997 ). On a grander scale, a stunning confirmation of these evolutionary predictions has come from an analysis of Saccharomyces cerevisiae (baker's yeast) and Caenorhabditis elegans (a worm). The genomes of both these organisms were sequenced very recently (Barrell 1996 ; Caenorhabditis elegans Sequencing Consortium 1998 ). The genes used by the yeast, a unicellular organism, are mostly genes dealing directly with core biochemical functions that all organisms must perform. From an evolutionary perspective, we would expect these genes to be ancient. Thus it was expected and shown that the worm contains a great majority of these genes. In contrast, the extra genes used by the worm, which deal with multicellularity, should be more recently evolved. Phylogenetic analysis has shown that this is exactly the case. The vast majority of extra genes in the worm appear to be directly derived from genes providing core cellular functions, in accordance with evolutionary prediction (Chervitz et al . 1998 ). An even larger study of the known eukaryotic genomes has further demonstrated that
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Molecular parahomology - Molecular parahomology The concept...

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