Nucleotide substitution: A?T.
The balltrip mutant has a nonsense mutation (AAA to TGA) resulting in truncation of the noncatalytic region.
Nucleotide substitution: A?G.
Amino acid replacement: K372term.
K372term
The reported Lys to stop amino acid change (AAA toTGA) requires substitution at more than one nucleotide position in the codon.
In female meiosis I, in balltrip mutants, one bipolar spindle is formed in only half of the spindles. In the other half, two or three bipolar spindles are formed and each associates with one or two bivalent chromosomes. Even when multiple spindles are formed, the morphology of each spindle appears to be normal, namely, a symmetrical bipolar spindle with focused poles. Abnormalities are restricted to the formation of multiple spindles, while other aspects are rarely affected in the balltrip mutant. However, a small minority (~6%) of balltrip spindles show loose microtubule bundling and/or unfocused spindle poles.
DNA staining reveals that early oocytes (at stage 6) in balltrip mutants exhibit a compact karyosome structure within the nucleus. At later stage (7 and 8), however, chromosomal DNA in the oocyte nucleus is often fragmented and/or a filamentous mass. The abnormality increases through the progression of stages. The balltrip mutation does no significantly affect other aspects of oogenesis, including specification of oocytes, polytenization in nurse nuclei, and the egg shape. The balltrip mutation is specifically defective in holding chromosomes together in prophase I and forming a single unified spindle in metaphase I.
balltrip mspsMJ208 double mutants remain female sterile (as balltrip). They exhibit a spindle phenotype identical to balltrip single mutants. About half of the oocytes contain two or three separate spindles, each of which is associated with bivalent chromosomes. Although the remaining oocytes contain one bipolar spindle shaped by an entire set of chromosomes, no tripolar spindles are seen (as in mspsMJ208 single mutants).
balltrip taccstella592 double mutants exhibit a phenotype identical to balltrip single mutants and no taccstella592 phenotype, indicating that balltrip is epistatic to taccstella592.
balltrip ncd1 double mutants exhibit a mixture of the ncd1 and balltrip phenotypes, namely, multiple spindles and unfocused poles.
