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Research has been conducted on quantitative trait loci. The contribution of the maternal and direct effect quantitative trait loci to early growth in mice has been investigated via the use of three-generation intercross of the small and large inbred mouse lineages, and the results are reported.

The [URE3] nonchromosomal genetic element is a prion of Ure2p, a regulator of nitrogen catabolism in Saccharomyces cerevisiae. Ure2[p.sup.1-65] is the prion domain of Ure2p, sufficient to propagate [URE3] in vivo. We show that full length Ure2p-green fluorescent protein (GFP) or a Ure2[p.sup.1-65]-GFP fusion protein is aggregated in cells carrying [URE3] but is evenly distributed in cells lacking the [URE3] prion. This indicates that [URE3] involves a self-propagating aggregation of Ure2p. Overexpression of Ure2[p.sup.1-65] induces the de novo appearance of [URE3] by 1,000-fold in a strain initially [ure-o], but cures [URE3] from a strain initially carrying the [URE3] prion. Overexpression of several other fragments of Ure2p or Ure2-GFP fusion proteins also efficiently cures the prion. We suggest that incorporation of fragments or fusion proteins into a putative [URE3] 'crystal' of Ure2p poisons its propagation.