THE MOUSE C1Q GENES ARE CLUSTERED ON CHROMOSOME-4 AND SHOW CONSERVATION OF GENE ORGANIZATION

Mouse complement component C1q is a serum glycoprotein which consists of six A chains, six B chains and six C chains. The three polypeptides are 223, 228, and 217 residues long, respectively, and are encoded by three genes. DNA probes for mouse C1q A, B, and C chains were hybridi zed to Southern blots of DNA obtained from various inbred mouse strain s. On the basis of fragment length polymorphisms, two different allele s of each of the genes could be identified. The distribution of these alleles was determined in the BXD and LXPL recombinant inbred strain s eries. Comparison with previously reported strain distribution pattern s shows that the genes encoding mouse C1q map to the same locus on dis tal chromosome 4. Overlapping clones spanning the entire gene cluster of C1q were isolated from genomic libraries using specific cDNA probes . The three genes C1qA, C1qB, and C1qC are closely arranged on a 19 ki lobase stretch of DNA in the 5' to 3' orientation A-C-B. Each gene con sists of two exons separated by one intron. Sequence comparison of C1q from three different species have shown that the B chains have the st rongest similarity. Southern blot analysis of chromosomal DNA from 14 vertebrate species demonstrated highest similarity between the C1qB ge nes, followed by C1qC and finally C1qA.