The segmentation gene runt is needed to activate Sex-lethal, a gene that controls sex determination and dosage compensation in Drosophila.

In Drosophila, sex is determined by the relative number of X chromosomes to autosomal sets (X:A ratio). The amount of products from several X-linked genes, called sisterless elements, is used to indicate to Sex-lethal the relative number of X chromosomes present in the cell. In response to the X:A signal, Sex-lethal is activated in females but remains inactive in males, being responsible for the control of both sex determination and dosage compensation. Here we find that the X-linked segmentation gene runt plays a role in this process. Reduced function of runt results in female-specific lethality and sexual transformation of XX animals that are heterozygous for Sxl or sis loss-of-function mutations. These interactions are suppressed by SxlM1, a mutation that constitutively expresses female Sex-lethal functions, and occur at the time when the X:A signal determines Sex-lethal activity. Moreover, the presence of a loss-of-function runt mutation masculinizes triploid intersexes. On the other hand, runt duplications cause a reduction in male viability by ectopic activation of Sex-lethal. We conclude that runt is needed for the initial step of Sex-lethal activation, but does not have a major role as an X-counting element.     

The rabbit muscle phosphofructokinase gene. Implications for protein structure, function, and tissue specificity

Sequence homologies between bacterial and rabbit muscle phosphofructokinases and between the amino- and carboxyl-terminal halves of the latter suggest that the mammalian enzyme evolved from a prokaryotic progenitor by gene duplication and divergence (Poorman, R. A., Randolph, A., Kemp, R. G., and Heinrikson, R. L. (1984) Nature 309, 467-469). We have isolated the gene for the rabbit enzyme and determined the nucleotide sequence for all the exons and most of the introns. This represents the first eukaryotic phosphofructokinase gene ever sequenced. The cloned gene is 17 kilobase pairs long. The coding sequence for 780 amino acids is split into 22 exons ranging in size from 15 to 63 codons. Sequence analysis shows that 75% of the bases at the third position of the codons in these exons are either G or C. Exons XV and XVI code for the 30 amino acid residues which were left unidentified in the published primary structure for this enzyme. When overlaid on the structure of the protein, most of the introns are located between or near the ends of the secondary structural elements but not at analogous positions in the two protein-coding halves of the gene.     

The cyclic nucleotide phosphodiesterase gene of Dictyostelium discoideum contains three promoters specific for growth, aggregation, and late development.

The cyclic nucleotide phosphodiesterase (phosphodiesterase) plays essential roles throughout the development of Dictyostelium discoideum. It is crucial to cellular aggregation and to postaggregation morphogenesis. The phosphodiesterase gene is transcribed into three mRNAs, containing the same coding sequence connected to different 5' untranslated sequences, that accumulate at different times during the life cycle. A 1.9-kilobase (kb) mRNA is specific for growth, a 2.4-kb mRNA is specific for aggregation, and a 2.2-kb mRNA is specific for late development and is only expressed in prestalk cells. Hybridization of RNA isolated from cells at various stages of development with different upstream regions of the gene indicated separate promoters for each of the three mRNAs. The existence of specific promoters was confirmed by fusing the three putative promoter regions to the chloramphenicol acetyltransferase reporter gene, and the analysis of transformants containing these constructs. The three promoters are scattered within a 4.1-kilobase pair (kbp) region upstream of the initiation codon. The late promoter is proximal to the coding sequence, the growth-specific promoter has an initiation site that is 1.9 kbp upstream of the ATG codon, and the aggregation-specific promoter has an initiation site 3 kbp upstream.     

Two amino acid residues confer type specificity to a neutralizing, conformationally dependent epitope on human papillomavirus type 11.

Characterization of virus binding by neutralizing antibodies is important both in understanding early events in viral infectivity and in development of vaccines. Neutralizing monoclonal antibodies (MAbs) to human papillomavirus type 11 (HPV11) have been described, but mapping the binding site has been difficult because of the conformational nature of key type-specific neutralization epitopes on the L1 coat protein. We have determined those residues of the L1 protein of HPV11 which confer type specificity to the binding of HPV11-neutralizing MAbs. Binding of three HPV11-specific neutralizing MAbs could be redirected to HPV6 L1 virus-like particles in which as few as two substitutions of corresponding amino acid residues from HPV11 L1 have been made, thus demonstrating the importance of these residues to MAb binding through the transfer of a conformationally dependent epitope. In addition, a fourth neutralizing MAb could be distinguished from the other neutralizing MAbs in terms of the amino acid residues which affect binding, suggesting the possibility that it neutralizes HPV11 through a different mechanism.