Both synchronous and asynchronous muscle isoforms of projectin (the Drosophila bent locus product) contain functional kinase domains

• Type of Material: Article
• Authors: A. Ayme-Southgate, Lehigh University; R. Southgate, Lehigh University; J. Saide, Boston University; Guy Benian, Emory University; M.L. Pardue, Massachusetts Institute of Technology
• Language: English
• Date: 1995-02-01
• Publisher: Rockefeller University Press
• Publication Version: Final Published Version
• Copyright Statement: © The Rockefeller University Press.
• Final Published Version (URL): http://dx.doi.org/10.1083/jcb.128.3.393
• Title of Journal or Parent Work: Journal of Cell Biology
• ISSN: 0021-9525
• Volume: 128
• Issue: 3
• Start Page: 393
• End Page: 403
• Grant/Funding Information: This work was supported by grants from National Institutes of Health (GM21874 to M. L. Pardue, AR39836 to G. M. Benian) and grant from National Science Foundation (MCB-9316975 to A. Ayme-Southgate) as well as by starting funds from Lehigh University (to A. Ayme-Southgate).
• Keywords: Cell Biology; MYOFIBRILLAR PROTEIN; Science & Technology; LEG MUSCLE; LIGHT CHAIN KINASE; SKELETAL-MUSCLE; Z-BAND; STRETCH-ACTIVATION; FIBRILLAR FLIGHT-MUSCLE; CAENORHABDITIS-ELEGANS; Life Sciences & Biomedicine; INSECT FLIGHT
• Research Categories: Biology, Physiology; Health Sciences, Pathology; Biology, Cell

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(D) 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(D) 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 l(4)2 was a complex (or pseudoallelic) locus.