Patterns of proteins synthesized in the R15 neuron of Aplysia. Temporal studies and evidence for processing.

Abstract

The time-course of changes in the pattern of newly synthesized proteins in the R15 neuron of the parietovisceral ganglion of A. californica was studied at 14.degree. C. Polyacrylamide gels (5%) containing sodium dodecyl sulfate (SDS) were used to separate newly synthesized (leucine-labeled) proteins from the neuron. The pattern of newly synthesized proteins from the R15 neuron does not change significantly if 5 h pulses of labeled leucine are given during the first 72 h of in vitro incubation of the excised ganglion. The leucine incorporation level begins to decline somewhere between 17-43 h after the ganglion is isolated; at 43 and 69 h the incorporation levels fall to 29 and 10% of the initial level, respectively. A number of conclusions were drawn from the use of a sequential, double-label type of experiment in the same cell. There is processing of SDS-soluble, 12,000-dalton (12 k) material to 6,000-9,000-dalton (6-9 k) material. These materials are the 2 major peaks on gels after long labeling periods and together account for about 35% of all newly synthesized proteins. After synthesis of 12 k material, there is a gradual disappearance of 12 k (half-life .apprx. 8 h) and simultaneous appearance of 6-9 k material on the gels, as the postsynthesis chase period of ganglia incubation is increased. The processing of 12 k to 6-9 k material occurs even in the presence of anisomycin, a protein synthesis inhibitor, during the chase period. While the rate of this conversion can vary from cell to cell, it appears to remain consistent within, and is characteristic of, any individual R15. No circadian rhythm is seen in either the rate of 12 k synthesis or the rate of 12 k to 6-9 k processing with 5 h label periods. Results are discussed in relation to the roles of 12 k and 6-9 k material in the R15 neuron.