The isozyme form of eukaryotic initiation factor 4F [eIF-(iso)4F] from wheat germ is composed of a p28 subunit that binds the 7-methylguanine cap of mRNA and a p86 subunit having unknown function. The p86 subunit was found to have limited sequence similarity to a kinesin-like protein encoded by the katA gene of Arabidopsis thaliana. Native wheat germ eIF-(iso)4F and bacterially expressed p86 subunit and p86-p28 complex bound to taxol-stabilized maize microtubules (MTs) Numerous studies have provided evidence for interactions between the cytoskeleton and the eukaryotic protein synthesis machinery. Polysomal mRNAs, ribosomes, and certain translation factors are associated with the cytoskeleton from detergent-extracted animal cells (1-4). Treatment of HeLa cells with the microfilament-disrupting agent cytochalasin releases mRNA, ribosomes, and initiation factors from the cytoskeletal framework (1, 3, 4). Polyribosomes have been found associated with cytoskeleton preparations from plants as well (5-7). Certain translation factors have been immunolocalized to the cytoskeleton of animal (8-10) and plant (11) cells. The translational machinery appears to have a relatively stable association with the cytoskeleton in animal cells, because detergentextracted cytoskeletons (12) and saponin-permeabilized cells (13) engage in efficient translation without the addition of macromolecular translation components. Thus, these observations indicate that the translational machinery may be bound to and regulated by the cytoskeleton.A different perspective is provided, however, by mounting evidence that protein synthesis factors may influence cytoskeletal function. For example, the existence of homologs of elongation factor la (EF-la) in putative centrosome precursor particles from CHO cells (14) and in microtubule (MT)-organizing centers of sea urchin mitotic spindles (15-17) suggests binding of EF-l1a to the minus ends of MTs and a function in MT nucleation. A similar MT-organizing role of a putative EF-la in tobacco cells was deduced from immuno-The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fact. localization patterns produced by antibodies against a sea urchin centrosomal EF-la homolog (11). However, animal EF-la was recently reported to sever MTs deficient in MTassociated proteins (MAPs) (18), a result we have confirmed with plant EF-la and MTs (L. E. Littlepage and L.C.M., unpublished data). Thus, these observations indicate that, under particular conditions, EF-la may modulate the disposition of MTs. Other than EF-la, however, no other translation factor has been demonstrated to affect MTs.The isozyme form of eukaryotic initiation factor 4F [eIF-(iso)4F] from wheat germ is composed of equimolar amounts of a small subunit (p28) that binds the 7-methylguanine (m7G) cap of mRNAs and a large subunit (p86) that has unknown function during translation and limited sequ...

Amiprophos-methyl (APM), a phosphoric amide herbicide, was previously reported to inhibit the in vitro polymerization of isolated plant tubulin (L.C. Morejohn, D.E. Fosket [1984] Science 224: 874-876), yet little other biochemical information exists concerning this compound. To characterize further the mechanism of action of APM, its interactions with tubulin and microtubules purified from cultured cells of tobacco (Nicofiana tabacum cv Bright Yellow-2) were investigated. Low micromolar concentrations of APM depolymerized preformed, taxol-stabilized tobacco microtubules. Remarkably, at the lowest APM concentration examined, many short microtubules were redistributed into fewer but 2.7-fold longer microtubules without a substantial decrease in total polymer mass, a result consistent with an end-to-end annealing of microtubules with enhanced kinetic properties. Quasi-equilibrium binding measurements showed that tobacco tubulin binds ['4C]oryzalin with high affinity to produce a tubulin-oryzalin complex having a dis- Phosphoric amide herbicides such as APM (Tokunol M) and butamiphos (Cremart) were developed as preemergence herbicides and are effective on annual grasses and broadleaf weeds (Aya et al., 1975). The uses of phosphoric amides are similar to those of the dinitroaniline herbicides, including