Intracellular transport of newly synthesized and mature proteins via vesicles is controlled by a large group of proteins. Here we describe a ubiquitous rat protein—endoplasmic reticulum (ER) and Golgi 30-kD protein (ERG30)—which shares structural characteristics with VAP-33, a 33-kD protein from Aplysia californica which was shown to interact with the synaptic protein VAMP. The transmembrane topology of the 30-kD ERG30 corresponds to a type II integral membrane protein, whose cytoplasmic NH₂ terminus contains a predicted coiled-coil motif. We localized ERG30 to the ER and to pre-Golgi intermediates by biochemical and immunocytochemical methods. Consistent with a role in vesicular transport, anti-ERG30 antibodies specifically inhibit intra-Golgi transport in vitro, leading to significant accumulation of COPI-coated vesicles. It appears that ERG30 functions early in the secretory pathway, probably within the Golgi and between the Golgi and the ER.

Inhibition of nerve fiber (neurite) formation by colchicine and Colcemid was studied in monolayer cultures of dissociated spinal ganglia of the chick. Replica cultures were fixed after appropriate incubation and alkaloid treatment. Quantitative estimates of the mean total neurite length per neuron (MNL) were made by use of camera lucida tracing. MNL values plotted against time of incubation gave control curves with an initial lag period, a phase of rapid increase, and a final phase in which MNL increase was retarded. Colchicine at 0.01–0.05 µg/ml (2.4 x 10^-8-1.2 x 10^-7 M) caused reversible, concentration dependent, inhibition of the increase in MNL when applied during the lag period or phase of rapid increase. At the highest concentration there was a net decrease in MNL. The effect of Colcemid at 0.05 µg/ml was similar to that of colchicine, but more rapidly reversible. In most experiments there was no loss of neurons during the period of inhibition of MNL increase by colchicine or Colcemid. Therefore selective destruction of neurons was not involved in the inhibition of neurite growth. Prolonged incubation after treatment with the highest concentration used resulted in a 50% loss of neurons, in part through detachment of viable cells. Quantitative radioautography of the alkaloid-treated neurons with leucine-¹⁴C indicated little or no inhibition of incorporation into protein during inhibition of MNL increase. The results strongly suggest that inhibition of neurite growth involves a specific effect of colchicine, presumably the disruption of microtubules. They are thus consistent with the hypothesis that the polymerization of microtubules is essential to the formation of nerve fibers.