A HEAT SHOCK-ACTIVATED CDNA RESCUES THE RECESSIVE LETHALITY OF MUTATIONS IN THE HETEROCHROMATIN-ASSOCIATED PROTEIN HP1 OF DROSOPHILA-MELANOGASTER

HP1 is a small nonhistone chromosomal protein of Drosophila melanogast er predominantly localized to the pericentric heterochromatin. We have shown previously that mutations in the HP1 coding sequences are assoc iated with dominant suppression of heterochromatic position-effect var iegation, and with recessive lethality. When fused to an Hsp70 heat sh ock gene promoter, the cDNA encoding HP1 supports the heat shock-induc ible accumulation of HP1 protein in transgenic flies; this cDNA constr uct complements the dominant suppression of position-effect variegatio n associated with mutations in the HP1 gene. Here, we report experimen ts demonstrating that the heat shock-driven HP1 cDNA is capable of ful ly rescuing the recessive lethality associated with HP1 mutations in a heat shock-dependent fashion. If heat shock-induced HP1 expression is delayed for as long as 5 days, more than half of the mutant flies sti ll survive until adulthood, consistent with a substantial maternal con tribution to embryonic and larval viability. Elevating HP1 levels as l ate as 7-8 days of development is sufficient to enhance variegation th reefold, suggesting that the extent of heterochromatic position effect can be modified subsequent to the initial appearance of HP1 in the nu clei of syncytial blastoderm embryos.