The mapping of a chromosomal region corresponding to much of a cytogenetic band, 1q32, is proposed. A master library of YAC clones of human DNA will be screened with probes from six genes in the Regulators of Complement Activation (RCA) locus and probes from the T200 gene, all of which map to the same bank in both mouse and man. Initial YAC clones will be restriction mapped, and portions of terminal fragments will be used as probes to isolate further clones that will create as continuous a map as possible. The genomic forms of the RCA and T200 genes will be individually analyzed for intron/exon structure, and nearby additional expressed genes will be sought as transcribed regions. These studies should permit an understanding of the extent of diversity and linkage of genes in this evolutionary conserved configuration; of the numbers of possible related genes encoding surface regulatory proteins; and thus of features of the evolution of the RCA multigene family from a simple structural motif.