Disease relevance of bt

• We propose that this hatching failure is due to muscle weakness caused by projectin defects [1].
• Identification of the domains for DNA binding and transactivation function of C protein from bacteriophage Mu [2].

High impact information on bt

• In contrast, the staining pattern of projectin, another IFM-I-band protein, was not altered by actin removal [3].
• Kettin along with projectin may constitute the elastic filament system of insect IFM and determine the muscle's high stiffness necessary for stretch activation [3].
• 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 [4].
• The projectin gene is in polytene region 102C/D where the bentD phenotype maps [4].
• 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 bentD breakpoint [4].

Biological context of bt

• Alternative splicing of an amino-terminal PEVK-like region generates multiple isoforms of Drosophila projectin [5].
• The lethal(4) 102 CDa mutant has a 141 nucleotide insertion containing stop codons in all three reading frames within an exon sequence, showing that it cannot synthesize normal projectin [1].
• Two mutants mapped to the location of the projectin gene in the 102C subdivision of chromosome 4, lethal(4) 102 CDa and bent-Dominant, have DNA rearrangements within their projectin gene [1].
• Assembly of the giant protein projectin during myofibrillogenesis in Drosophila indirect flight muscles [6].
• We report here that Drosophila has a single-copy gene containing the two-motif amino acid sequence pattern that characterizes twitchin and titin [7].

Anatomical context of bt

• Here, we show that Duf/Kirre and its interaction partners Rols7 (found in founder myoblasts and growing myotubes) and Sns (found in fcms) are organized in a ring-structure at the contact points of fcms with precursor cells, while cytoskeletal components like F-actin and Titin are centered in this ring in both cell types [8].
• This supports the idea that interactions of projectin with other Z-band associated proteins are sufficient for its initial assembly into the forming myofibrils [6].
• In this study we found that projectin is oriented within the IFM sarcomere with its NH(2)-terminus embedded in the Z-bands [9].
• The characterization of twitchin in the obliquely striated muscles of Caenorhabditis elegans is reported and the deductions made from its amino acid sequence are considered [10].

Associations of bt with chemical compounds

• This analysis led also to the identification of a domain rich in the amino acids P, E, V and K within the NH(2) terminus of projectin [5].
• Projectin has a serine/threonine protein kinase activity [11].
• The entire cDNA sequences of projectin isoforms of crayfish claw closer and flexor muscles and their localization [12].

Co-localisations of bt

• Correspondingly, projectin is found in association with forming Z-bands during pupation and colocalizes with alpha-actinin and kettin [13].

Other interactions of bt

• Drosophila projectin is an extremely large protein found within the muscle sarcomeric unit, parallel with the actin and myosin filaments [5].
• In contrast, treatment of adult myofibrils with calpain, which removes the Z-bands, does not lead to the release of projectin [6].
• Initial in vitro binding assays indicate interactions of several projectin regions with themselves and myosin heavy chain [13].
• On Lowicryl sections of asynchronous flight muscle, indirect immunogold staining has localized alpha-actinin and the 210-kD protein throughout the matrix of the Z-band, projectin between the Z- and A-bands, and the 400/600-kD components at the I-band/Z-band junction [14].

Analytical, diagnostic and therapeutic context of bt

• Here, we describe the completion of the projectin sequence analysis, which defines projectin as a 1 MDa protein, composed of 39 immunoglobulin and 39 fibronectin III domains [5].
• METHODS: We performed immunofluorescence studies on Drosophila pupal tissue squashes and isolated myofibrils to identify the pattern of appearance and assembly for projectin and several other myofibrillar proteins, using both wild type and mutant fly stocks [6].
• To identify the regions of C protein important for its function, deletion and site-directed mutagenesis were carried out [2].

References