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Heat‐shock genes coding for heat‐shock protein 70 (HSP70) in Drosophila melanogaster were subcloned into an SV40/plasmid recombinant capable of replication in permissive monkey COS cells. Following transfection of COS cells, no significant amount of Drosophila hsp70 RNA was detected at 37 degrees C. In contrast, a heat‐shock at 43 degrees C or arsenite poisoning at 37 degrees C induced the massive production of Drosophila hsp70 RNA of correct size and faithful 5′ ends. After heat‐shock, the efficiency of hsp70 transcription in COS cells containing 2‐4 X 10(4) gene copies was found to be 15‐30% of that measured in Drosophila, on a per gene basis. By testing a series of 5′ deletion mutants in this inducible transcription assay it was found that a sequence less than 70 bp long, directly upstream of the hsp70 gene, was essential for the heat or arsenite induction of transcription.

Abstract. In Drosophila, the large muscle protein, projectin, has very different localizations in synchronous and asynchronous muscles, suggesting that projectin has different functions in different muscle types. The multiple projectin isoforms are encoded by a single gene; however they differ significantly in size (as detected by gel mobility) and show differences in some peptide fragments, presumably indicating alternative splicing or termination. We now report additional sequence of the projectin gene, showing a kinase domain and flanking regions highly similar to equivalent regions of twitchin, including a possible autoinhibitory region. In spite of apparent differences in function, all isoforms of projectin have the kinase domain and all are capable of autophosphorylation in vitro. The projectin gene is in polytene region 102C/D where the bent ° phenotype maps. The recessive lethality of bent D is associated with a breakpoint that removes sequence of the projectin kinase domain. We find that different alleles of the highly mutable recessive lethal complementation group, l(4)2, also have defects in different parts of the projectin sequence, both NH2-terminal and COOH-terminal to the bent ~ breakpoint. These alleles are therefore renamed as alleles of the bent locus. Adults heterozygous for projectin mutations show little, if any, effect of one defective gene copy, but homozygosity for any of the defects is lethal. The times of death can vary with allele. Some alleles kill the embryos, others are larval lethal. These molecular studies begin to explain why genetic studies suggested that 1(4)2 was a complex (or pseudoallelic) locus.

All striated muscles respond to stretch by a delayed increase in tension. This physiological response known as stretch-activation is, however, predominately found in vertebrate cardiac muscle and insect asynchronous flight muscles. Stretch-activation relies on an elastic third filament system composed of giant proteins known as titin in vertebrates or kettin and projectin in insects. The projectin insect protein functions jointly as a 'scaffold and ruler' system during myofibril assembly, and as an elastic protein during stretch activation. An evolutionary analysis of the projectin molecule could potentially provide insight into how distinct protein regions may have evolved in response to different evolutionary constraints. We mined candidate genes in representative insect species from Hemiptera to Diptera, from published and novel genome sequence data and carried out a detailed molecular and phylogenetic analysis. The general domain organization of projectin is highly conserved, as are the protein sequences of its two repeated regions-the Immunoglobulin type C and Fibronectin type III domains. The conservation in structure and sequence is consistent with the proposed function of projectin as a scaffold and ruler. In contrast, the amino acid sequences of the elastic PEVK domains are noticeably divergent although their length and overall unusual amino acid makeup are conserved. These patterns suggest that the PEVK region working as an unstructured domain can still maintain its dynamic, and even its three-dimensional properties, without the need for strict amino acid conservation. Phylogenetic analysis of the projectin proteins also supports a reclassification of the Hymenoptera in relation to Diptera and Coleoptera

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