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Cancer Research Campaign, Cell Cycle Genetics Group, Department of Anatomy and Physiology, University of Dundee,
Dundee DD1 4HN, Scotland
abnormal spindle, a gene required for normal
spindle structure and function in Drosophila melanogaster, lies immediately adjacent the gene tolloid at
96A/B. It encodes a 220-kD polypeptide with a predicted pI of 10.8. The recessive mutant allele asp1 directs the synthesis of a COOH terminally truncated or
internally deleted peptide of ~124 kD. Wild-type Asp
protein copurifies with microtubules and is not released
by salt concentrations known to dissociate most other
microtubule-associated proteins. The bacterially expressed NH2-terminal 512-amino acid peptide, which has a number of potential phosphorylation sites for
p34cdc2 and MAP kinases, strongly binds to microtubules. The central 579-amino acid segment of the molecule contains one short motif homologous to sequences
in a number of actin bundling proteins and a second
motif present at the calmodulin binding sites of several
proteins. Immunofluorescence studies show that the
wild-type Asp protein is localized to the polar regions
of the spindle immediately surrounding the centrosome. These findings are discussed in relation to the
known spindle abnormalities in asp mutants.
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