Tyrosine tRNA was isolated from bovine liver and its nucleotide sequence was determined using in vitro 32p_ labeling techniques. Several important structural features of the tRNA are: the presence of gal-Q in the first position of the anticodon, acp3U at position 20, and a pair of adjacent N,N-dimethylguanosines (residues 26 and 27). A human DNA fragment harbored in a lambda phage clone was isolated, and restriction enzyme analysis revealed the presence of three tRNA genes in a 6.0-kb BamHI subfragment. Portions of the 6.0-kb DNA fragment containing the tRNA genes were sequenced by the method of Maxam and Gilbert and analyzed for transcriptional activity in vitro using homologous cytoplasmic extracts. A threonine tRNAUGU gene exhibited high transcriptional activity dependent on its 5'- flanking sequence. The enhanced transcription is not completely inhibited by alpha-amanitin. The value of studying tRNA structure in concert with the cognate tRNA. genes is discussed.

The physiological significance of noradrenergic sympathohabenular ingrowth following medial septal lesions was investigated. Following septal lesions, sympathetic fibers originating in the superior cervical ganglia are known to sprout into the medial habenular nuclei, and into the hippocampal formation. Previous work involving sympathohippocampal ingrowth showed that firing rates in septal animals with no ingrowth showed that firing rates in septal animals with no ingrowth were higher than rates of septal animals with ingrowth and controls. Those results suggested that sympathetic ingrowth in the hippocampus had some functional capability in a modulatory manner. The primary aim of the present study was to determine if the peripheral sympathetic ingrowth into the medial habenular nuclei following a septal lesion is functionally significant. The results showed that firing rates of neurons of the medial habenulae in animals receiving septal lesions were significantly higher than rates of control animals and septal lesioned + ganglionectomized animals.