No abstract

The kinesin superfamily is a large group of proteins (kinesin-like proteins [KLPs]) that share sequence similarity with the microtubule (MT) motor kinesin. Several members of this superfamily have been implicated in various stages of mitosis and meiosis. Here we report our studies on KLP67A of Drosophila. DNA sequence analysis of KLP67A predicts an MT motor protein with an amino-terminal motor domain. To prove this directly, KLP67A expressed in Escherichia coli was shown in an in vitro motility assay to move MTs in the plus direction. We also report expression analyses at both the mRNA and protein level, which implicate KLP67A in the localization of mitochondria in undifferentiated cell types. In situ hybridization studies of the KLP67A mRNA during embryogenesis and larval central nervous system development indicate a proliferation-specific expression pattern. Furthermore, when affinity-purified anti-KLP67A antisera are used to stain blastoderm embryos, mitochondria in the region of the spindle asters are labeled. These data suggest that KLP67A is a mitotic motor of Drosophila that may have the unique role of positioning mitochondria near the spindle.

The concentration of cyclin B transcripts at the posterior pole of the Drosophila oocyte occurs at a late stage of oogenesis and is dependent on the sequence in the 3′ untranslated part of the RNA. These transcripts become incorporated into the pole cells of the developing embryo and persist through a subsequent period of embryogenesis in which these cells are not dividing. We show that RNA injected into the posterior cytoplasm of syncytial embryos accumulates in the pole cells if it contains sequences present in the 3′ untranslated region of maternal cyclin B transcripts. The injected RNA is not translated until a point prior to the resumption of mitosis by these cells, once they have become incorporated into the gonads. Zygotic transcription directed from the cyclin B promoter does not begin in the pole cells until the first instar larva has hatched. Deletion of a small sequence element from the 3′ untranslated region of an epitope tagged cyclin B RNA does not affect its posterior accumulation but results in its premature translation.