Southern Hybridization Analyses of Somatic Cell Hybrids Reveal That Human BB1 Is a Member of a Multigene Family Dispersed Throughout the Human Genome and Appears to be Linked to the Human G25K Genes

The hBBl RNA (2.3 kb in length) encodes a 57-amino-acid protein whose production is essential for cellular transit of G_! phase of the cell cycle (Moats-Staats etal., 1994). Homology searches of GenBank and EMBL revealed that bases 1–234 of the hBBl cDNA were 97% homologous to the 3′ terminal 234 bases of the g25K cDNA (bases 940–1,175, Shinjo et al., 1990) the human homolog of the yeast cdc42 cDNA. We have used the techniques of the long-range polymerase chain reaction (PCR) (Barnes, 1994) and Southern hybridization analyses of a somatic cell hybrid panel to investigate hBBl gene structure and to determine whether the hBBl gene(s) overlaps the g25K gene. These studies have demonstrated that the hBBl RNA is encoded by a gene family composed of eight members that is dispersed throughout the human genome localizing under high-stringency conditions to chromosomes 1, 4, 7, 8, and 20. We have also determined that two hBBl gene(s) and two g25K gene(s) map to similar-size Bam HI restriction fragments on chromosomes 4 and 7.