The non-dosage compensated LSP1-alpha gene of Drosophila melanogaster lies immediately downstream of the dosage compensated L12 gene.

The X-linked gene LSP1-alpha of Drosophila melanogaster, expressed in the third larval instar, does not exhibit dosage compensation at its normal locus but does compensate when it is relocated to ectopic sites on the X chromosome. A transcription unit designated L12, which is active in the second larval instar and capable of encoding a putative protein of 28.5 kDa, lies immediately downstream from LSP1-alpha. We have determined that L12 is dosage compensated by measuring the steady-state level of its transcript in male and female larvae. The difference in response of these two adjacent genes should be taken into consideration when models of the mechanism of dosage compensation are formulated.