Titus M A, Wessels D, Spudich J A, Soll D
Department of Cell Biology, Stanford University School of Medicine, California 94305.
Mol Biol Cell. 1993 Feb;4(2):233-46. doi: 10.1091/mbc.4.2.233.
The myoA gene of Dictyostelium is a member of a gene family of unconventional myosins. The myosin Is share homologous head and basic domains, but the myoA gene product lacks the glycine-, proline-, alanine-rich and src homology 3 domains typical of several of the other myosin Is. A mutant strain of Dictyostelium lacking a functional myoA gene was produced by gene targeting, and the motility of this strain in buffer and a spatial gradient of the chemoattractant cyclic AMP was analyzed by computer-assisted methods. The myoA- cells have a normal elongate morphology in buffer but exhibit a decrease in the instantaneous velocity of cellular translocation, an increase in the frequency of lateral pseudopod formation, and an increase in turning. In a spatial gradient, in which the frequency of pseudopod formation is depressed, myoA- cells exhibit positive chemotaxis but still turn several times more frequently than control cells. These results demonstrate that the other members of the unconventional myosin family do not fully compensate for the loss of functional myoA gene product. Surprisingly, the phenotype of the myoA- strain closely resembles that of the myoB- strain, suggesting that both play a role in the frequency of pseudopod formation and turning during cellular translocation.
盘基网柄菌的肌动蛋白基因A是非常规肌球蛋白基因家族的成员。肌球蛋白I类具有同源的头部和碱性结构域，但肌动蛋白基因A的产物缺乏其他几种肌球蛋白I类典型的富含甘氨酸、脯氨酸、丙氨酸的区域和src同源3结构域。通过基因打靶产生了一种缺乏功能性肌动蛋白基因A的盘基网柄菌突变株，并通过计算机辅助方法分析了该菌株在缓冲液和趋化因子环磷酸腺苷的空间梯度中的运动性。肌动蛋白基因A缺失的细胞在缓冲液中具有正常的伸长形态，但细胞移位的瞬时速度降低，侧向伪足形成的频率增加，转弯次数增加。在伪足形成频率降低的空间梯度中，肌动蛋白基因A缺失的细胞表现出正向趋化性，但仍然比对照细胞多转几圈。这些结果表明，非常规肌球蛋白家族的其他成员不能完全补偿功能性肌动蛋白基因A产物的缺失。令人惊讶的是，肌动蛋白基因A缺失菌株的表型与肌动蛋白基因B缺失菌株的表型非常相似，这表明两者在细胞移位过程中伪足形成和转弯的频率中都起作用。
