Abstract
The multigene family which codes for the mouse major urinary proteins (MUPs) consists of approximately 35 genes. Most of these are members of two different groups, Group 1 and Group 2, which can be distinguished by nucleic acid hybridisation. By screening a Charon 4A library of mouse DNA with probes from the 5'-flanking region of a MUP gene, we have isolated clones that contain both a Group 1 and a Group 2 gene, orientated in a divergent fashion, with 15 kb of DNA between the 5' ends of the genes. We show that this pairwise arrangement is the predominant organisation of MUP genes in the BALB/c genome. We argue that the head-to-head gene pair is the unit both of DNA organisation and of evolution. Taking into account the genes themselves, the intervening 15 kb and the homologous 3'-flanking regions, this unit is approximately 45 kb long. We also show that some MUP genes may be linked in a tail-to-tail fashion with 26-28 kb between the 3' ends of two genes. This suggests that the minimum distance between successive 45-kb units is approximately 7 kb.