An osmosensing signal transduction pathway in yeast.

Yeast genes were isolated that are required for restoring the osmotic gradient across the cell membrane in response to increased external osmolarity. Two of these genes, HOG1 and PBS2, encode members of the mitogen-activated protein kinase (MAP kinase) and MAP kinase kinase gene families, respectively. MAP kinases are activated by extracellular ligands such as growth factors and function as intermediate kinases in protein phosphorylation cascades. A rapid, PBS2-dependent tyrosine phosphorylation of HOG1 protein occurred in response to increases in extracellular osmolarity. These data define a signal transduction pathway that is activated by changes in the osmolarity of the extracellular environment.

Genes with specific functions in the ovarian follicles of Calliphora erythrocephala (Diptera).

Working with the large dipteran Calliphora erythrocephala, we have performed differential screening to identify genes actively expressed in the previtellogenic and early vitellogenic stages of oogenesis but silent during the early stages of embryogenesis. Clones containing sequences homologous to four such genes have been characterized. Two clones are homologous to the yolk protein 1 gene of Drosophila melanogaster. These two clones are expressed not only in the columnar follicle cells surrounding the oocyte but also in the border cells--a highly specialized subgroup of the follicle cells. This indicates a new function for these cells though previously to contribute mainly in the formation of the micropyle. A third clone, which is related to the D. melanogaster vitelline membrane protein genes of the cluster at chromosomal locus 26A, is expressed only in the perioocyte follicle cells and not the border cell population. The fourth clone encodes a sequence of unknown function which is abundantly expressed in the germ line cells of the follicle. Transcripts homologous to this clone persist into the mature follicle and initially appear concentrated at the anterior pole of the oocyte. The distribution of repetitious DNA within these four clones indicates that the C. erythrocephala genome has a short interspersion arrangement of repetitive DNA.

A second maternally expressed Drosophila gene encodes a putative RNA helicase of the "DEAD box" family.

Recently, a family of proteins containing the conserved motif Asp-Glu-Ala-Asp, the "DEAD box" proteins, has been identified. This family is typified by the eukaryotic translation initiation factor eIF4A, and its members are believed to share the functional property of ATP-dependent RNA unwinding. One of the previously identified members of this family (vasa) is the product of a maternally expressed gene from Drosophila melanogaster that is known to play a role in the formation of the embryonic body plan. We report here the isolation of a Drosophila gene that has an mRNA expression pattern somewhat similar to that of vasa and also encodes a DEAD box protein. We have termed this gene ME31B to reflect its maternal (ovarian germ-line) expression and its location within the 31B chromosome region. Comparisons with the other members of this family reveal that although ME31B is most like the protein Tif1/Tif2, which probably represents the Saccharomyces cerevisiae version of eIF4A, it is unlikely that ME31B represents the Drosophila eIF4A protein per se. A search for mutations in the ME31B gene has established that the P element which causes the female-sterile mutation flipper lies in the 3' flank of the ME31B gene.