Characterization of a Constitutive Variant of the Murine Serum Protein Allotype, Slp

Abstract

Properties of the Ss serum protein (putatively the murine homologue of the fourth component of complement) and its allotypic form, Slp, were studied in a wild-derived variant, Ss^w7. The Ss^w7 allele is unique in that it confers non-sexlimited expression of the Slp allotype. During examination of the H-2 haplotypes of two congenic lines which derived their Ss^w7 allele from a common origin, it was found that intra-H-2 recombination had occurred during the establishment of one of these lines. The sex-limited expression of Slp as determined by the Ss^d allele was constrasted in several ways to the constitutive expression of Slp as determined by the Ss^w7 allele. Slp expression in mice carrying the Ss^d allele was found to be subject to control by the testicular feminization mutant, Tfm, while in mice carrying Ss^w7 the Slp expression was independent of Tfm control. This implies that Slp is subject to a rather fundamental hormonal control mechanism in mice carrying Ss^d and presumably all other Slp-positive Ss alleles, with the exception of Ss^w7. It is proposed that Ss^w7 may represent an “operator-constitutive” mutation of the Jacob-Monod type. Including the Ss^w7 allele, there are now at least seven distinguishable Ss variants. Each of these Ss alleles is characterized by a unique level of Ss and/or Slp antigenic expression. The sex-limitation difference and quantitative differences in Ss and Slp expression associated with the Ss^w7 allele were found to be codominant or intermediate when Ss^w7 was in heterozygous combinations with other Ss alleles. This indicates a lack of trans effects and argues against genetic differences in regulatory proteins as the basis for these polymorphisms.