Analysis of multiple restriction fragment length polymorphisms of the gene for the human complement receptor type I. Duplication of genomic sequences occurs in association with a high molecular mass receptor allotype.

Abstract

Human CR1 exhibits an unusual form of polymorphism in which allotypic variants differ in the molecular weight of their respective polypeptide chains. To address mechanisms involved in the generation of the CR1 allotypes, DNA from individuals having the F allotype (250,000 Mr), the S allotype (290,000 Mr), and the F' allotype (210,000 Mr) was digested by restriction enzymes, and Southern blots were hybridized with CR1 cDNA and genomic probes. With the use of Bam HI and Sac I, an additional restriction fragment was observed in 20 of 21 individuals having the S allotype with no associated loss of other restriction fragments. Southern blot analysis with a noncoding genomic probe derived from the S allotype-specific Bam HI fragment showed hybridization to this fragment and to two other fragments that were also present in FF individuals. Thus, an intervening sequence may be repeated twice in the F allele and three times in the S allele. A restriction fragment length polymorphism (RFLP) unique to two individuals expressing the F' allotype was seen with Eco RV, but the absence of persons homozygous for this rare allotype prevented further comparisons with the F and S allotypes. Analysis of the CR1 transcripts associated with the three CR1 allotypes indicated that these differed by 1.3-1.5 kb and had the same rank order as the corresponding allotypes. Taken together, these findings suggest that the S allele was generated from the F allele by the acquisition of additional sequences, the coding portion of which may correspond to a long homologous repeat of approximately 1.4 kb that has been identified in CR1 cDNA. We saw two other RFLPs with Hind III and Pvu II that were in linkage dysequilibrium with the Bam HI-Sac I RFLPs associated with the S allotype, and a third polymorphism was seen with Eco RI that was not in linkage dysequilibrium with the other polymorphisms. Thus, 10 commonly occurring CR1 alleles can be defined, making this locus a useful marker for the long arm of chromosome 1 to which the CR1 gene maps.

Identification of distinct C3b and C4b recognition sites in the human C3b/C4b receptor (CR1, CD35) by deletion mutagenesis.

“…The probes used for screening cDNA libraries study were CRI-1 (9) (American Type Culture Collection, accession No . 57331), CRI-2 (9), CRI-4 (10), and CRI-18, a 252-bp Sau 3AI fragment from the 0 .5-kb Eco RI fragment of cDNA clone XH3 .1 corresponding to nucleotides 101-352 in Fig . 1 .…”

Structure of the human CR1 gene. Molecular basis of the structural and quantitative polymorphisms and identification of a new CR1-like allele.

“…High or low CRl expression on erythrocytes was associated with allelic 7 .4and 6.9-kb genomic Hind III fragments, respectively (25,26) . Linkage dysequilibrium was observed between this RFLP and the CR1 structural allotypes, suggesting that this polymorphism was located within or near the CRI gene (19,24,25) . The present study examines the molecular bases of these structural and genomic polymorphisms by mapping the CRI gene and localizing the restriction sites that determine these RFLPs.…”

Complement Receptor 1: Disease associations and therapeutic implications

“…These are not post-translational modifications as their unglycosylated primary transcript possesses the same variation (Lublin et al, 1986). The genomic difference between each allotype ranges from 1.3 to 1.5 kb, equivalent to a single LHR (Wong et al, 1986. The insertion-deletion mechanisms due to unequal crossing over of chromosomes have been considered responsible for such a variation .…”