THE MURINE POLYCOMB-GROUP GENE EED AND ITS HUMAN ORTHOLOGUE - FUNCTIONAL IMPLICATIONS OF EVOLUTIONARY CONSERVATION

Similar to Drosophila, murine Polycomb-group (PcG) genes regulate ante rior-posterior patterning of segmented axial structures by transcripti onal repression of homeotic gene expression. The murine PcG gene eed ( embryonic ectoderm development) encodes a 441-amino-acid protein with five WD motifs which, except for the amino terminus, is highly homolog ous to Drosophila ESC (Extra Sex Combs). Here, sequence and expression analysis as well as chromosomal mapping of the human orthologue of ee d is described. Absolute conservation of the human eed protein along w ith significant divergence at the nucleotide level reveals functional constraints operating on all residues. The human orthologue appears to be ubiquitously expressed and maps to chromsome 11q14.2-q22.3. Using the first WD motif of the P-subunit of the bovine G protein as a struc tural reference, the predicted locations of two previously identified eed point mutations (A, Schumacher et al,, 1996, Nature 383: 250-253) are also reported herein, The proline substitution (L196P) in the seco nd WD motif of the 17Rn5(3354SB) null allele maps to the internal core of the inner end of the P-propeller blade and is likely to disrupt pr otein folding. In contrast, the asparagine substitution (I193N) in the second WD motif of the hypomorphic 17Rn5(1989SB) allele maps onto the surface of the P-propeller blade near the central cavity and may affe ct surface interactions without compromising propeller packing. These results illustrate the critical importance of all residues for eed fun ction in mammals and support a model whereby the amino terminus might implement function(s) related to embryonic development in higher organ isms. (C) 1998 academic Press.