Expression of p2M

Mouse 3,M is encoded by a single gene per haploid genome, indicating that the same 3iM gene encodes the light chain of the various class I proteins, CD1 and intestinal Fc receptors. The 32M gene consists of four exons, with the majority of the protein-coding sequence (amino acids 3-95), within a single exon (exon II). All types of interferon (IFN) (a, 3 and y), of which IFNy is usually the most potent, and tumor necrosis factor a (TNFa) have been shown to induce or increase expression of both chains of class I molecules in a wide variety of cell types. For 32M this is thought to occur by both transcriptional and post-transcriptional events. The expression of the 3iM gene has been thought to be related to that of the class I heavy chain by sharing common regulatory mechanisms. However, the expression of these genes follows a different time course during embryogen-esis; the synthesis of 32M is first detectable at the two-cell stage, while class I heavy chain mRNA is detectable after the midsomite stage on gestation day 9 in the mouse embryo. This suggests that expression of these genes is not always coordinately regulated. It has been shown in some embryonic carcinoma cell lines that expression of class I MHC proteins can be induced by driving the cells from an undifferentiated state to a differentiated state, and that transcription of both the 32M and class I heavy chain genes is activated by this induction. A transcriptional enhancer activity has been found in the 5' flanking sequence of the mouse 32M gene. This enhancer may have at least two important regions, one of which shows sequence similarity to the H-2 enhancer (class I regu-

Figure 1 The residues forming the domain interfaces are highlighted in color on the C" backbone stereogram. Filled and colored C" atoms make contacts s4 A. Red, a,, a2 residues in interface with fS?M; green, (32M residues in interface with a,a2; blue a3 residues in interface with p2M; yellow, fi2M residues in interface cn3', pink, (»,«2 residues in interface with orange, a3 residues in interface with a-,a2. (A) A view perpendicular to ct,ct2 pseudodyad with the binding cleft viewed end-on (^012-013 interface not shown). (B) A side view with the molecule rotated 90° about the pseudodyad (a3-p2M interface not shown). (C) A drawing of the @2M residues (blue) interacting underneath the a^ 3 sheet. a,o<2 Residues in (32M interface are in red; those in c*3 interface with small green labels. Hatched region highlights the pleat under which p2M side-chains Phe-B56 and Trp-B60 make van der Waals' contacts with a,a2. (Reprinted with permission from Saper MA, Bjorkman PJ and Wiley DC (1991) Refined structure of the human histocompatibility antigen HIA-A2 at 2.6 A resolution. Journal of Molecular Biology 219: 277-319.) (See also color Plate 9.)

Figure 1 The residues forming the domain interfaces are highlighted in color on the C" backbone stereogram. Filled and colored C" atoms make contacts s4 A. Red, a,, a2 residues in interface with fS?M; green, (32M residues in interface with a,a2; blue a3 residues in interface with p2M; yellow, fi2M residues in interface cn3', pink, (»,«2 residues in interface with orange, a3 residues in interface with a-,a2. (A) A view perpendicular to ct,ct2 pseudodyad with the binding cleft viewed end-on (^012-013 interface not shown). (B) A side view with the molecule rotated 90° about the pseudodyad (a3-p2M interface not shown). (C) A drawing of the @2M residues (blue) interacting underneath the a^ 3 sheet. a,o<2 Residues in (32M interface are in red; those in c*3 interface with small green labels. Hatched region highlights the pleat under which p2M side-chains Phe-B56 and Trp-B60 make van der Waals' contacts with a,a2. (Reprinted with permission from Saper MA, Bjorkman PJ and Wiley DC (1991) Refined structure of the human histocompatibility antigen HIA-A2 at 2.6 A resolution. Journal of Molecular Biology 219: 277-319.) (See also color Plate 9.)

Figure 1 Continued.

latory element, CRE) region 1. Both this p2M sequence and region I of the H-2 enhancer bind the nuclear factors KBF1 and H2TF1.

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