Kinesin-Ii, Coming and Going

UKARYOTIC cells are constantly challenged with a variety of transport problems.These are encountered during membrane trafficking, distribution of mitochondria and other membrane-bounded organelles, mRNA localization, and during special events such as mitosis and meiosis.Much of this transport is mediated by the concerted efforts of kinesins, dyneins, and myosins, the molecular motors that operate along the cytoskeletal network of microtubules and actin filaments.Differentiated cells generate special transport needs, such as the long distance axonal transport of materials in neuronal cells, the bidirectional intraflagellar transport of proteinaceous rafts in ciliated cells, and the dispersion and aggregation of pigment granules in melanophores.One motor protein that has been adapted to operate in these three specialized movements is kinesin-II, also known as the heterotrimeric kinesin, KIF3A/3B, and KRP 85/95 .This paper briefly summarizes two independent studies that (a) identify a normally soluble enzyme as a cargo of kinesin-II during anterograde axonal transport (Ray et al., 1999), and (b) indicate that kinesin-II is carried as a cargo during retrograde intraflagellar transport within neuronal sensory cilia (Signor et al., 1999a).