The localization of connexin43 (Cx 43) in rat kidney was investigated by the indirect immunofluorescence technique with polyclonal antisera raised against Cx 43. Cx 43 is a gap junction protein expressed in a variety of tissues. The typically punctuated gap junction immunofluorescence (GJI) was observed in the renal arterial and arteriolar system. In the renal artery the GJI was concentrated in the media. In the juxtamedullary nephrons, the GJI is particularly abundant in the vascular bundles. There is abundant GJI in the extraglomerular mesangium while in the afferent arteriole GJI appears decreased. Abundant GJI was observed in the inner medullary collecting ducts and pelvic epithelium. The localization of Cx 43 immunofluorescence observed in this study is only in partial agreement with the results of ultrastructural investigations on the distribution of gap junctions in the kidney. An extensive tight junctional system has been demonstrated in the collecting duct system. However, gap junctions have been reported to be absent. Further studies to resolve this discrepancy are required.

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 DrosophUa 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 ME3JB 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 Tifl/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 ME3JB gene has established that the P element which causes the female-sterile mutation flipper lies in the 3' flank of the ME3JB gene.Recently a family of proteins that function as ATP-dependent RNA helicases has been identified (1).These proteins share a domain of about 370 amino acids in which a series of highly conserved motifs are arranged in identical order and with very similar spacing. Two of these conserved sequences represent specialized versions of the A and B motifs previously recognized in other ATP-binding proteins (2,3). The four-amino-acid sequence Asp-Glu-Ala-Asp (DEAD) is part ofthe specialized version ofthe B motif. These "DEAD box" proteins derive from organisms across all evolutionary orders (Escherichia coli to mouse), and for some of them, genetic and molecular studies have provided indications as to their functions in vivo (4-7). Thus this family of proteins appears to be involved in a wide range of intracellular events in which alteration of RNA secondary structure must play a critical role. These include formation of the initiation complex for mRNA translation, mRNA splicing, and ribosome biosynthesis. Functionally, the eukaryotic translation initiation factor eIF4A, which is the archetypal member of the family, is the one best understood at the molecular level (8-10).

The early growth response gene, Egr-1, is up-regulated transiently by mitogens and many other stimuli in all cells tested. Using NIH3T3 cells conditionally expressing v-sis from a metallothionein promoter, we show that the addition of Zn2+ stimulates the production of PDGF-B (v-sis) and elicits the expression of Egr-1 in a dose-dependent and time-regulated manner. The signal is likely independent of protein kinase C, but depends on tyrosine kinase and other kinase activities and is mediated by c-Ha-Ras since the presence of dominant-negative mutants of Ras and Raf abrogates the induction of Egr-1 expression by Zn2+. Transiently activated Ras expression in NIH3T3 cells also stimulates the transient expression of Egr-1, but cells that constitutively express Ras do not have elevated levels of Egr-1. Transient assays also demonstrated that Zn2+ or activated Ras expression stimulate the activity of a 950 bp Egr-1 promoter-reporter gene construct and this is abrogated in the presence of mutant Ras and Raf. The accumulated data show that Egr-1 gene expression is regulated by multiple mechanisms, as would be needed for putative roles in cell proliferation, in suppression of transformation and in differentiation.

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