The murine Ia alpha chains, E alpha and A alpha, show a surprising degree of sequence homology.

Abstract

The I region of the murine major histocompatibility complex codes for a group of glycoproteins, the Ia antigens, thought to be involved in the control of immune responsiveness. Each Ia antigen complex contains a "heavy chain,": a-"light chain," and the "invariant chain." We describe here the isolation and characterization ofgenomic and cDNA clones for one ofthe heavy chains, Ak. The complete nucleotide sequence of the cDNA clone is presented, and the predicted amino acid sequence is compared with that of another e chain, Ek. About 50% of the amino acids are identical, a finding somewhat unexpected on the basis of preliminary protein sequence data.The mouse major histocompatibility complex (MHC) codes for a variety ofcell-surface antigens thought to be important in cellcell recognition, especially in an immunological context (1, 2). Among these cell-surface molecules are the Ia antigens, glycoproteins that map to the I region ofthe MHC and that appear to control the ability ofan animal to mount an effective response to certain foreign antigens (1, 2). Two different Ia antigen complexes have been described thus far: the A complex is composed oftwo subunits, Aa (Mr, 34,000) and A,3 (Mr, 29,000), which map to the I-A subregion; the E complex consists of E. (Mrv 34,000), which maps to the I-E subregion, and E,3 (Mr) 29,000), which maps to I-A. The invariant chain, Ii, is found in both A and E complexes, but its structural gene does not map to the MHC (1, 2). As of yet, structural information about the la antigens remains scant; in particular, it has proven very difficult to obtain protein sequence data. Therefore, we have exploited the techniques of molecular genetics in the hope of determining more rapidly the structural organization of these immunologically important cell-surface molecules.We describe here the isolation-and identification ofa genomic and cDNA clone for the murine Ak gene. The complete nucleotide sequence ofthe cDNA clone is presented, and the predicted amino acid sequence of the A' protein is compared with that of the Ea gene product (unpublished data). This analysis reveals a surprising similarity between the two gene products.(The A, and Ea genes were cloned from "a" haplotype mice.Because mice of the a haplotype are actually "k" haplotype in the I region, we refer to the genes as Ak and Ek throughout the paper.) MATERIALS AND METHODS Mice. B10.AKM mice were purchased from The Jackson Laboratories. C. S. David of the Mayo Clinic, Rochester, MN, provided the B10. MBR mice. All other mouse strains were produced in our breeding colony at Stanford. GenomicCloning. An A/J thymus DNA genomic library was produced in Charon 4 k phage by described methods (3). Briefly, high molecular weight A/J thymus DNA was partially digested with EcoRI, the digest was size-fractionated on a sucrose gradient, a 20-kilobase (kb) fraction was isolated and ligated to the purified EcoRI-cut arms of Charon 4, and the ligation mix was packaged and used to infect Escherichia coli C600. One million clones were screened...

Sequence analysis and structure-function correlations of murine q, k, u, s, and f haplotype I-A beta cDNA clones.

“…cDNA libraries from B10.A (Ia"), B10.PL (Ia"), A.TH (Ias), B10.G (Iaq), and B10.M (Iaf) mice were provided by D. Mathis and C. Benoist and have been described (6,7). Screening for I-Ak clones was done with a human DQp cDNA clone (8).…”

Isolation and characterization of a cDNA clone for the murine I-E beta polypeptide chain.

“…Construction of a cDNA library from spleens of B10.A mice has been described (19). The library was screened with a full-length human DR,3 cDNA clone, 2918.4 (unpublished data) by the method of Benton and Davis (20).…”

Identification of a new component in the murine Ia molecular complex.

“…One approach designed to address this issue is to obtain detailed information on the structure of these antigens to determine what structural features can account for the observed biological properties of Ia. Newly developed techniques in molecular biology have allowed rapid advances in our knowledge of the primary structure of the class II gene products (3)(4)(5). This methodology does not, however, provide information on the structural features of Ia that are generated posttranslationally, features that may play a role in Ir gene function or in regulation of Ia antigen expression.…”