Retroviral reverse transcriptase possesses DNA polymerase and ribonuclease H (RNase H) activity within a single polypeptide. Chemical or proteolytic treatment of reverse transcriptase has been used in the past to produce enzyme that is missing DNA polymerase activity and retains RNase H activity. It has not been possible to obtain reverse transcriptase that lacks RNase H but retains DNA polymerase activity. We have constructed a novel deletion derivative of the cloned Moloney murine leukemia virus (M-MLV) reverse transcriptase gene, expressed the gene in E. coli, and purified the protein to near homogeneity. The purified enzyme has a fully active DNA polymerase, but has no detectable RNase H activity. These results are consistent with, but do not prove, the conclusion that the DNA polymerase and RNase H activities of M-MLV reverse transcriptase reside within separate structural domains.

Serine protease gene fragments approximately 480 nucleotides in length were amplified from Ctenocephalides felis larval and adult cDNA libraries using degenerate oligonucleotide PCR primers. Partial clones of thirty-eight distinct serine protease encoding sequences were isolated, and nineteen different full-length cDNAs encoding mature serine proteases were subsequently cloned and sequenced. All of the mature proteases contained the histidine, aspartic acid and serine amino acids of the catalytic triad characteristic of serine proteases. The mature C. felis serine proteases had amino acid sequences that were at most 29-53% identical to those known insect and arachnid serine proteases. Two of the C. felis gene sequences had similarity with the Drosophila melanogaster developmental genes snake and stubble. mRNA expression of selected serine protease genes was examined in different life stages, tissues, genders, and in response to bloodfeeding.

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Genomic clones of human and porcine choline acetyltransferase were obtained by screening genomic libraries with synthetic oligonucleotides. The human and porcine genes exhibit significant conservation of both their intron/exon structure and the nucleotide sequence in their 5' flanking regions. However, the two genes differ in several respects, including the absence of a "TATA" box in the human gene and differences in the position of the methionine start codon. Analysis of the promoter region of the two genes has led to the localization of an enhancer element that appears necessary for efficient transcription of the gene.

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