Axoplasmic Transport of Transfer RNA in the Chick Optic System

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Abstract
It has previously been shown that 4S RNA is transported in the optic nerve of the chick, but that no movement of rRNA can be detected. The 4S component behaved as though it were composed mainly of transfer RNA (tRNA), but the possibility remained that it could contain significant amounts of material resulting from RNA degradation. The transport of this 4S component has been examined in more detail to determine its nature. In addition, the transported material was examined to establish whether the transport of tRNA is a general phenomenon or that there are only a limited number of species involved. This was done using the same principles applied in the previous study; i.e., the specific activities of separated 4S RNA species appearing in the optic tectum 4 days after intraocular injection of [3H]uridine were compared with that of 5S RNA, a nontransported species. The separation was accomplished using 2.8‐5‐10‐17% slab polyacrylamide gels, and 18 separate regions of 4S species could be identified. The results show that at least most, if not all 4S RNA species are transported. In a separate series of experiments the 4S RNA was aminoacylated and again separated on slab gels. In this instance, the RNA was labelled with [3H]uridine and the aminoacyl component with [14C]amino acids. Gel profiles of these dual‐labelled components showed excellent correspondence between the two labels, demonstrating that 4S RNA species could be aminoacylated and were therefore tRNA species. In contrast to tRNA, the small‐molecular‐weight RNA (smwRNA), species L (7S RNA) is not transported. This smwRNA is largely cytoplasmic in location, as is tRNA. If the transport system were nonspecific it would be expected that smw‐L would also be transported. A number of potential roles for axonal tRNA are considered.