Homology units

Wen D, Peles E, Cupples R, Suggs SV, Bacus SS, et al. 1992. Neu differentiation factor A transmembrane glycoprotein containing an EGF domain and an immunoglobulin homology unit. Cell 69 559-572. 

Human ceruloplasmin is composed of a single polypeptide chain of 1046 amino acid residues. The protein shows a threefold internal homology of amino acid sequence and each homology unit contains 340-350 amino acids. From these data, it is suggested that ceruloplasmin is an evolutionary product of a tandem triplication of ancestral gene. 

The qualifying feature of the immunoglobulin homology unit is its molecular architecture. Delineation of this structure has resulted from a considerable amount... 

Figure 2. Structural homologies between the blood clotting proteins. The lengths of the bars represent the sizes of the polypeptide chains. Homology units include , disulfide ring CC, coiled-coil region Y-carboxyglutamic acid-containing...

The N-terminal half of the L chain is known as the variable, or Vl region the C-terminal half is the Cl segment (C for constant). Terms used to designate the individual, 110- to 120-residue segments, are domain or homology unit. ... 

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