Genetic Analysis of the Drosophila 63F Early Puff: Characterization of Mutations in E63-1 and maggie, a Putative Tom22

Abstract

The 63F early puff in the larval salivary gland polytene chromosomes contains the divergently transcribed E63-1 and E63-2 ecdysone-inducible genes. E63-1 encodes a member of the EF-hand family of Ca2+-binding proteins, while E63-2 has no apparent open reading frame. To understand the functions of the E63 genes, we have determined the temporal and spatial patterns of E63-1 protein expression, as well as undertaken a genetic analysis of the 63F puff. We show that E63-1 is expressed in many embryonic and larval tissues, but the third-instar larval salivary gland is the only tissue where increases in protein levels correlate with increases in ecdysone titer. Furthermore, the subcellular distribution of E63-1 protein changes dynamically in the salivary glands at the onset of metamorphosis. E63-1 and E63-2 null mutations, however, have no effect on development or fertility. We have characterized 40 kb of the 63F region, defined as the interval between Ubi-p and E63-2, and have identified three lethal complementation groups that correspond to the dSc-2, ida, and mge genes. We show that mge mutations lead to first-instar larval lethality and that Mge protein is similar to the Tom22 mitochondrial import proteins of fungi, suggesting that it has a role in mitochondrial function.

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“…The calcium-binding protein e63-1 transcript codes for a calcium-binding protein orthologous to the E63-1 protein in Drosophila. Expression of this protein is induced by 20-hydroxy ecdysone signaling in developing salivary glands ( Andres and Thummel, 1995 ), but it has also been shown to be expressed in other larval tissues regardless of hormone regulation ( Vaskova et al, 2000 ). The DNA-binding protein d-ets-4 transcript encodes a transcription factor orthologous to Drosophila ets98b .…”