The l(3)S12 locus of Drosophila melanogaster: heterochromatic position effects and stage-specific misexpression of the gene in P element transposons.

l(3)S12 is a vital locus whose function is required in embryos, early larvae, late pupae and oogenesis. We have identified a cold-sensitive allele, l(3)S12(3), and characterized conditional misexpression of the gene associated with this mutation as well as with several euchromatic insertions of l(3)S12+ transposons. Surviving cold-sensitive mutants as well as underexpression variants generated by P element transformation display a phenotypic syndrome that can include delayed development, abnormal bristle morphology, and female sterility. Using these phenotypes, defects in putative "early" and "late" l(3)S12 expression can be identified. The sensitivity of certain l(3)S12+ insertions to site-specific euchromatic position effect appears to be due to separation of the gene from an endogenous enhancer element during cloning. This enhancerless construct can be used to identify and perhaps to select "permissive" euchromatic sites, presumably adjacent to enhancer elements, which in some cases permit elevated production not only of the l(3)S12 message, but also of a P element-l(3)S12 fusion transcript. Certain of these permissive sites appear to control stage-specific expression, and we propose that this system may be used to identify, clone, and characterize such loci. Heterochromatic position effect on this locus has been demonstrated. Available evidence suggests that the l(3)S12 gene may be involved in protein synthesis, perhaps encoding a ribosomal protein.