DIFFERENTIAL EXPRESSION DURING EMBRYOGENESIS OF 3 GENES CLUSTERED IN THE RAS1 REGION OF DROSOPHILA-MELANOGASTER

Transcription mapping and nucleotide sequence analysis reveal that the genomic region of the Drosophila Ras1 gene contains a cluster of thre e closely localized genes, A gene termed Rlb1 is located nearby and up stream of Ras1, and is oriented in the opposite polarity relative to R as1. In addition, a third gene termed Rlc1, is found at a very close p roximity downstream to Rlb1. Ras1, the homologue of the human transfor ming ras genes, has been shown to be active in the posterior termini o f the Drosophila embryo and in the eye imaginal disc in pathways of ce ll fate determination. We demonstrate that during embryogenesis Ras1 t ranscripts are restricted mainly to the embryonic central nervous syst em, suggesting that the gene product also may have a role in these ner ve cells. Rlb1 encodes for a novel, lysine-rich basic protein. It is e xpressed mainly in the developing midgut and in the somatic mesoderm. Rlc1 also encodes for a novel, basic protein. The expression of Rlc1 d uring embryogenesis is similar, but not identical, to the expression p attern detected for Ras1. The vertebrate p21(Ras) proteins are bound t o the inner face of the cell membrane. Ras1, the Drosophila homologue of p21, and the Rlb1 protein, are also non-cytoplasmic, membranous pro teins. Rlb1 is found in the cell membrane of larval midgut epithelial cells. In addition, Rlb1 is detected in the nuclei of these cells, and in the nuclei of the midgut imaginal cells. (C) 1994 Wiley-Liss, Inc.