Mapping of a mouse homolog of a Heterochromatin protein gene to the X Chromosome

Modifiers of position-effect-variegation inDrosophila are thought to encode proteins that are either structural components of heterochromatin or enzymes that modify these components. We have recently shown that a sequence motif found in oneDrosophila modifier gene, Heterochromatin protein 1 (HP1), is conserved in a wide variety of animal and plant species (Singh et al. 1991). Using this motif, termed chromo box, we have cloned a mouse candidate modifier gene,M31, that also shows considerable sequence homology toDrosophila HP1. Here we report evidence of at least four independently segregating loci in the mouse homologous to theM31 cDNA. One of these loci—Cbx-rsl—maps to the X Chromosome (Chr), 1 cM proximal toAmg and outside the X-inactivation center region.