PHYSICAL LINKAGE AND ORIENTATION OF THE HUMAN-COMPLEMENT C8-ALPHA ANDC8-BETA GENES ON CHROMOSOME 1P32

Human C8 is one of five components (C5b, C6, C7, C8, C9) of the cytoly tic C5b-9 complex of complement. It consists of three nonidentical sub units (C8 alpha, C8 beta, C8 gamma), which are encoded in separate gen es. Genetic linkage and chromosomal localization studies previously es tablished that C8 alpha and C8 beta are closely linked on chromosome 1 p32. In this study, clones with inserts containing genes for both C8 a lpha and C8 beta were isolated from a yeast artificial chromosome (YAC ) human genomic DNA library and characterized in an effort to determin e intergenic distance and orientation. One clone with a similar to 330 -kb insert yielded restriction digest patterns for C8 alpha and C8 bet a that agreed with those obtained previously from digests of human gen omic DNA, thereby confirming the presence of intact copies of both gen es. A second clone with a similar to 280-kb insert yielded similar res ults; however, it was truncated at the 5' end of the C8 alpha gene. Re striction digests of both clones were subjected to PFGE and Southern b lot analysis using probes specific for the terminal exons of C8 alpha (exons 1 and 11) and C8 beta (exons 1 and 12). Results indicate the ge nes are physically linked (< 23 kb) and in a 3' - 3' orientation. This is the same orientation as the ancestrally related C6 and C7 genes, w hich are also physically linked on chromosome 5p13.