The black-pearl gene of Drosophila defines a novel conserved protein family and is required for larval growth and survival

Using a transposon insertion line of the Drosophila Genome Project we have cloned the black-pearl gene (blp) analyzed cDNA clones, generated various m utants, and characterized their phenotypes. The blp, gene codes for a prote in of 15.7 kDa calculated molecular weight that has been conserved from yea st to plants and mammals with high homology. A domain of these new proteins shows distant similarity to DnaJ domains indicating a functionally relevan t interaction with other proteins. The P element insertion in line P1539 li es within the 5' untranslated leader of the black-pearl gene. Flies homozyg ous for this insertion are semi-lethal, escapers produce very few offspring and show melanotic inclusions in the hemocoel ('black pearls') similar to various melanotic 'tumor' mutants. Two small deletions confined to the blp gene and two EMS-induced mutations are homozygous lethal. These null mutant s appear normal up to a prolonged first instar larval stage but fail to gro w and die. Thus in Drosophila the blp, gene is specifically required for la rval growth. The evolutionary conservation in both unicellular and multicel lular organisms suggests for the new protein family described here a fundam ental role in cell growth. (C) 2001 Elsevier Science B.V. All rights reserv ed.