Biology Reference
In-Depth Information
duplication and functional divergence of a type I keratin gene might lead to a spe-
cific type II gene duplication being selectively favored.
Genes of the major histocompatibility complex.
The major histocompatibility
complex (MHC) region on chromosome 6p21.3 spans 4 Mb DNA and contains the
genes encoding the human leukocyte antigens (HLA), a large family of cell surface
glycoproteins (
Figure 4.18
). The function of the MHC proteins, members of the
immunoglobulin superfamily (Section 4.2.4,
Immunoglobulin genes
), is to present
peptides to T cells. The MHC family is divided into classes I and II whose members
differ in terms of their structure, function, expression and polymorphism (Hughes,
1996). Class I molecules (the classical transplantation antigens) are expressed on
most cells whereas the expression of class II molecules is confined to antigen-pre-
senting cells. Both class I and II molecules are heterodimers with four extracellular
domains;
1,
2 and
3 associated with
2-microglobulin (class I) and
1,
2,
1
and
2 (class II). These molecules bind both self- and pathogen-derived peptides in
a surface groove (
peptide-binding region
) and present these to cytotoxic T cells that
lyse the pathogen-infected cell, thereby limiting host infection.
Table 4.4.
Types of human keratin and the genes that encode them
Keratin type
Gene
Chromosomal location
Keratin 1
KRT1
12q11-q13
Keratin 2A
KRT2A
12q11-q13
Keratin 3
KRT3
12q12-q13
Keratin 4
KRT4
12p12-q11
Keratin 5
KRT5
12q
Keratin 6A
KRT6A
12q12-q21
Keratin 6B
KRT6B
12
Keratin 7
KRT7
12q12-q21
Keratin 8
KRT8
12
Keratin 9
KRT9
17q21
Keratin 10
KRT10
17q21-q23
Keratin 12
KRT12
17q11-q12
Keratin 13
KRT13
17q21-q23
Keratin 14
KRT14
17q12-q21
Keratin 15
KRT15
17q21-q23
Keratin 16
KRT16
17q12-q21
Keratin 17
KRT17
17q12-q21
Keratin 18
KRT18
12q11-q13
Keratin 19
KRT19
17q21-q23
Keratin, hair, acidic 1
KRTHA1
17q12-q21
Keratin, hair, acidic 2
KRTHA2
17q12-q21
Keratin, hair, acidic 3A
KRTHA3A
17q12-q21
Keratin, hair, acidic 3B
KRTHA3B
17q12-q21
Keratin, hair, acidic 4
KRTHA4
?
Keratin, hair, acidic 5
KRTHA5
17q12-q21
Keratin, hair, basic 1
KRTHB1
12q13
Keratin, hair, basic 2
KRTHB2
?
Keratin, hair, basic 3
KRTHB3
12q12-q13
Keratin, hair, basic 4
KRTHB4
?
Keratin, hair, basic 5
KRTHB5
12q12-q13
Keratin, hair, basic 6
KRTHB6
12q13
