The following information accompanied stocks donated to the Bloomington Stock Center by Thomas Cline, University of California at Berkeley.
SxlM8 is a fully constitutive Sxl allele whose constitutive character cannot be modified by mutations in other genes that affect pre-mRNA splicing. It is a 110 bp deletion that eliminates bases +9212 through +9321 relative to the transcription start site of the "maintenance" promoter, taking out both of the 3' splice sites of the male-specific Sxl exon, as well as the polypyrimidine tract that those splice sites depend on. Consequently, the fully female pre-mRNA Sxl splicing pattern occurs by default in this allele, regardless of X chromosome dose, and the gene is fully constitutive from the moment that the "establishment" promoter is active. The allele was recovered in the sisA suppressor screen described in:
Barbash, D.A. and T.W. Cline, 1995 Genetic and molecular analysis of the autosomal component of the primary sex determination signal of Drosophila melanogaster. Genetics 141: 1451-1471 (FBrf0084726)
but the allele was described and characterized in the Ph.D. thesis of Daniel Barbash:
Barbash, D. A., 1995 Genetic and molecular analysis of suppressors of the Drosophila melanogaster female-specific lethal mutation sisterlessA. University of California at Berkeley. (FBrf0084727)