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Thyrotropin-releasing hormone (TRH) is an important extracellular signal substance that acts as a hypothalamic-releasing factor, which stimulates the release of adenohypophyseal hormones and functions as a neurotransmitter/neuromodulator in the central and peripheral nervous system. The Inactivation ofTRH after its release is catalyzed by an ectoenzyme localized preferentially on (14). The particulate peptidase is localized in synaptosomal (11) and adenohypophyseal (15) membrane fractions. In brain-derived cells in culture, it is found only on the surface of neuronal cells but not on glial cells (16-18). In the pituitary the enzyme is localized preferentially on lactotrophs (17), and recent studies have demonstrated that the activity of the adenohypophyseal enzyme is regulated by estradiol (19) and is stringently controlled by thyroid hormones (20)(21)(22).After solubilization by limited proteolysis under very mild conditions, we recently succeeded in purifying the enzyme from rat and pig brain (about 200,000-fold) to electrophoretic homogeneity. In this report we describe the isolation and sequence of a cDNA encoding the TRH-degrading ectoenzyme.J Furthermore, we present information on the transcriptional regulation of the adenohypophyseal enzyme by thyroid hormones as well as on the functional expression of this peptidase in transfected mammalian cells.MATERIALS AND METHODS Enzyme Fragmentation and Peptide Sequencing. After isolation from rat or pig brain as described elsewhere (23)

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As with many other fungi, including the budding yeast Saccharomyces cerevisiae, the dimorphic fungus Candida albicans encodes the novel translation factor, elongation factor 3 (EF-3). Using a rapid affinity chromatography protocol, EF-3 was purified to homogeneity from C. albicans and shown to have an apparent molecular mass of 128 kDa. A polyclonal antibody raised against C. albicans EF-3 also showed cross-reactivity with EF-3 from S. cerevisiae. Similarly, the S. cerevisiae TEF3 gene (encoding EF-3) showed cross-hybridization with genomic DNA from C. albicans in Southern hybridization analysis, demonstrating the existence of a single gene closely related to TEF3 in the C. albicans genome. This gene was cloned by using a 0.7 kb polymerase chain reaction-amplified DNA fragment to screen to C. albicans gene library. DNA sequence analysis of 200 bp of the cloned fragment demonstrated an open reading frame showing 51% predicted amino acid identity between the putative C. albicans EF-3 gene and its S. cerevisiae counterpart over the encoded 65-amino-acid stretch. That the cloned C. albicans sequence did indeed encode EF-3 was confirmed by demonstrating its ability to rescue an otherwise non-viable S. cerevisiae tef3:HIS3 null mutant. Thus EF-3 from C. albicans shows both structural and functional similarity to EF-3 from S. cerevisiae.