SUMMARYIn Drosophila melanogaster x D. simulans hybrids, the alcohol dehydrogenase (ADH) electromorphs characteristic of the two parents display tissue-and stage-specific differences in relative level of expression. This implies distinct cis-acting regulatory elements associated with the respective Adh alleles. These cis-acting elements account in part, but not completely, for markedly different overall patterns of ADH expression in the two species. The regulatory patterns seem to be adaptively significant since they correlate with species-specific patterns of ethanol tolerance. The activity differences are accounted for by different levels of enzyme protein, but the underlying mechanisms have not been fully analysed and may be complex. Independent evolution of various aspects of the ADH developmental programme may relate to use of different promoters for transcription of the Adh locus in different developmental contexts. This system illustrates the potential importance of regulatory genes in evolution and provides a model for investigating the molecular basis of evolved regulatory differences.

The DNA sequence of a 3886-bp genomic region containing the alcohol dehydrogenase (Adh) gene from Drosophila affinidisjuncta, and the RNA sequences of the D. affinidisjuncta Adh transcripts, are presented. These data support the conclusion that two Adh promoters generate distinct, developmentally regulated Adh transcripts. Correlations between these sequences and the transcription map are discussed. Comparisons between these and equivalent data from D. melanogaster are also presented. We note the following observations: (1) Except at the extreme 3' end, the two genes are identically organized. (2) Drosophila Adh protein accumulates amino acid replacements at the rate of approximately 0.5 per million years. (3) Among the non-protein-coding DNA sequences, putative homologies occur in the two promoter regions.

No abstract

No abstract

Plasmids in 39 strains of Erwinia stewartii were examined by agarose gel electrophoresis. Most virulent strains had from 11 to 13 plasmids ranging in molecular mass from 2.8 to 210 megadaltons and contained plasmids of 210, 70, 49, 43, 29.5, 16.8, 8.8, and 2.8 megadaltons. Plasmids in strains SW2 and SS104 were characterized by both electron microscopy and agarose gel electrophoresis and may be useful as convenient references for sizing plasmids by electrophoresis. Specific size classes of plasmids could not be associated with antibiotic and heavy metal resistance, carbohydrate utilization, bacteriocin production, or pathogenicity to corn. However, avirulent strains tended to have fewer plasmids than virulent strains. Erwinia stewartii (E. F. Smith) Dye can cause a devastating disease of both sweet and field com. The bacterium grows in the intercellular spaces of leaves, causing localized lesions, and in the xylem vessels, causing systemic wilting. During the summer, E. stewartii is transmitted by the corn flea beetle (Chaetocnema pulicularia Melch) and can overwinter in the beetle's alimentary tract. We have been using E. stewartii as a model system for studying mechanisms of virulence and host resistance and have previously demonstrated that it readily exchanges Rfactors with Escherichia coli (5) and contains several derepressed conjugative plasmids which can mobilize pCR1 between E. stewartii and E. coli (6). The purpose of this study was to verify that the DNA species previously observed in strains SW2 and SS104 by agarose gel electrophoresis (AGE) (5, 6) are plasmid DNAs, to show that multiple plasmids are characteristic of this species, and to identify, for future study, size classes of plasmids common in virulent strains. MATERIALS AND METHODS Bacterial strains. E. stewartii strains that were analyzed for plasmids are given in Table 1. All E. coli R-plasmids and strain V517 were obtained from E. M.