RNA viruses show high mutation frequencies partly because of a lack of the proofreading enzymes that assure fidelity of DNA replication. This high mutation frequency is coupled with high rates of replication reflected in rates of RNA genome evolution which can be more than a millionfold greater than the rates of the DNA chromosome evolution of their hosts. There are some disease implications for the DNA-based biosphere of this rapidly evolving RNA biosphere.

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Juvenile hormones (JH) are a class of regulatory sesquiterpenoids that control metamorphosis in immature insects and reproduction in adult insects. The regulation of JH synthesis by the corpora allata (CA), a pair of endocrine glands with nervous connections to the brain, is achieved by a complex interplay of stimulatory and inhibitory factors mediated in part by the brain. The neuropeptide, allatotropin (Mas AT), was recently isolated and sequenced from the brain of the tobacco hornworm Manduca sexta. Mas AT is a 13-residue amidated peptide that activates JH synthesis in adult, but not larval, lepidopteran CA. A 23-nucleotide degenerate oligonucleotide was designed based on the peptide sequence and was used to isolate the Mas AT genomic clone. The Mas AT gene is expressed as three mRNAs which differ from one another by alternative splicing. These mRNAs are predicted to encode three distinct prohormones, each containing Mas AT. A restriction fragment from the genomic clone was then used to isolate the cDNA clone. In situ hybridization and immunohistochemistry studies show that Mas AT is expressed in both the central and enteric nervous systems. Cells expressing Mas AT were identified in the brain, frontal ganglion and terminal ganglion.

The nucleotide sequence of the tumor morphology locus, tms, from pTiA6NC has been determined. The sequence analysis indicates that each of two polyadenylylated transcripts encoded by this locus contains an open reading frame; the predicted transcript 1 gene product has a molecular size of 83,769 daltons, and the predicted transcript 2 gene product, of 49,588 daltons. The precise start and stop positions of the transcript 2 RNA have been mapped with S1 nuclease. Several insertion mutations have been constructed. One of these localizes the transcript 2 promoter within the 72 base pairs 5' to transcription initiation. Significant homology was observed between the protein encoded by transcript 1 and the adenine binding region of p-hydroxybenzoate hydroxylase from Pseudomonasfluorescens, suggesting that the transcript 1 protein binds adenine either as substrate or cofactor.

Eclosion hormone (EH) is a neuropeptide that triggers the performance of ecdysis behaviors at the end of a molt. We have isolated the EH gene from Drosophila melanogasfer, and localized the gene to the right arm of chromosome 3 at band position 90B1-2. The 97-amino-acid translation product contains a signal peptide followed by a 73-amino-acid prohormone. The N-terminus of the prohormone has diverged from lepidopteran EH both in its length and amino acid composition, and contains a potential endoproteolytic cleavage site. The deduced sequence of Drosophila EH is 58% identical (36 of 62 amino acids) to that of Manduca EH. The EH gene is expressed as a 0.8-kb transcript in a single pair of brain neurons which extend their processes the entire length of the central nervous system and also to the corpora cardiaca portion of the ring gland. These cells show massive depletion of immunoreactive EH at ecdysis.Over the last 10 years, work in invertebrates in general and insects in particular has led to identification of a large number of neuropeptides, many of which are expressed in a small number of cells within the central nervous system (CNS) [l, 21. These findings raise a number of important questions such as the role of these peptides in the normal physiology and development of the organism and the mechanisms that restrict peptide expression to a select set of cells within the CNS. To answer both questions, Drosophila melunogaster provides a number of distinct advantages. Mutants in a desired gene can be generated with relative ease and P-element transformation technology allows examination of regulatory regions that control peptide expression [3, 41. Consequently, we have turned to Drosophila to further our analysis of the neuropeptide eclosion hormone (EH), that triggers ecdysis of insects [5].Eclosion hormone was first found in moths [6] and later shown to be a 62-amino-acid peptide [7 -91 produced by two pairs of ventromedial neurosecretory cells in the brain [lO-131. In moths it has marked behavioral and developmental actions. It is known to act directly on the CNS to release the stereotyped motor programs that bring about the shedding of the old cuticle at the end of each molt [14]. Circulating peptide also acts on peripheral tissues to cause a diverse set of effects such as an increase in plasticity of wing cuticle [15], discharge of secretion by dermal glands [16], and the programmed degeneration of ecdysial muscles [17]. Yet the full range of EH actions are not known because it is not possible to block selectively either release or action of EH in moths. It appeared feasible to study EH in Drosophila because CNS extracts of both Calliphora [5] and Drosophila (Kimura and Truman, unpublished data) show EH activity in moth bioassays. Moreover, blood from ecdysing fleshflies, Sarcophaga bullata, stimulates premature ecdysis behavior in pharate (before ecdysis) flies [18]. The recent cloning of the EH gene from two species of moths, Munduca sexfa [ll] and Bombyx mori [13], has provided an avenue to search for t...

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