Figure 2.

Molecular map of the upd region. The map indicates the position of phages from the chromosomal walk, in kilobases. The positions of alleles that delimit the extent of the upd locus are shown beneath the chromosome, with bold lines indicating deleted DNA. Broken lines indicate uncertainties in the exact position of breakpoints. The position of transcription units is indicated at bottom. The 1-kb transcript has not been precisely mapped and falls within the indicated area. The 2.5-kb RNA is expressed only during late embryogenesis (after 13 hr), and the 1-kb RNA is present maternally, and again late in embryogenesis. The upd candidate transcript, 2.2 kb, is expressed during early zygotic stages (also see Fig. 3). CREB is shown for reference (porc is off the map at right). Proximal is to the right. Identification of single site lesions in two upd alleles, upd^YM55 and upd^YC43, confirms the assignment of these mutations to the same complementation group. Because these mutations fail to complement os alleles and only affect the protein encoded by the 2.2-kb transcript (Fig. 4), we conclude that os and upd are separable functions of the same locus. The breakpoints of os^4-51-1, os^c18, and os¹⁰⁹ (all os⁻, upd⁺) map at least 13 kb from the 2.2-kb transcript, suggesting that the os phenotype may derive from the disruption of an enhancer that lies far from the 3′ end of the upd transcript.