Wiskott-Aldrich syndrome protein physically associates with Nck through Src homology 3 domains

In the second of a series of experiments designed to identify p47nck-Src homology 3 (SH3)-binding molecules, we report the cloning of SAKAP II (Src A box Nck-associated protein II) from an HL60 cDNA expression library. This molecule has been identified as a cDNA encoding the protein product of WASP, which is mutated in Wiskott-Aldrich syndrome patients. Studies in vivo and in vitro demonstrated a highly specific interaction between the SH3 domains of p47nck and Wiskott-Aldrich syndrome protein. Furthermore, anti-Wiskott-Aldrich syndrome protein antibodies recognized a protein of 66 kDa by Western blot (immunoblot) analysis. In vitro translation studies identified the 66-kDa protein as the protein product of WASP, and subcellular fractionation experiments showed that p66WASP is mainly present in the cytosol fraction, although significant amounts are also present in membrane and nuclear fractions. The main p47nck region implicated in the association with p66WASP was found to be the carboxy-terminal SH3 domain.

Physical association between Src homology 3 elements and the protein product of the c-cbl proto-oncogene

To investigate the nature of proteins recognized by Src homology 3 (SH3) domains, a cDNA expression library was prepared from macrophages and screened with a probe representing the three SH3 domains of p47nck. Two clones were isolated, and one, designated SAKAP I (for Src A box Nck-associated protein I), contained the carboxyl-terminal half of the cbl proto-oncogene product. Studies in vitro demonstrated reactivity between SAKAP I and SH3 domains derived from a variety of molecules. Wide variations in this assay suggested a high degree of specificity inherent in SAKAP I binding. Moreover, it was possible to demonstrate an in vivo association between p47nck and p120c-cbl in HL60 cells. These findings suggest that proteins containing SH3 elements regulate Cbl function.

Diverse biologic properties imparted by the c-fgr proto-oncogene

The c-fgr proto-oncogene specifies a nonreceptor protein-tyrosine kinase, p55c-fgr, a member of the src family. In the present study, we have mutagenized c-fgr to mimic alterations found at the 3' end of the v-fgr oncogene and have investigated the biologic effects of normal and mutant p55c-fgr expression. Genes lacking 10 or 13 codons at the 3' end, as well as a gene encoding phenylalanine instead of tyrosine at codon 523, were potent oncogenes when transfected into NIH 3T3 cells. Specific enzymatic activities of the more highly transforming gene products were 3-4-fold greater than that of p55c-fgr. In vivo, the amount of tyrosine phosphorylation of cellular proteins was directly proportional to potency in focus-forming assays. These findings are the first to identify highly transforming mutations of the c-fgr proto-oncogene. The proto-oncogene was also active in transforming assays, demonstrably greater than that of a kinase-deficient mutant. Foci arising in c-fgr-transfected cultures expressed abundant enzyme that was normal by a number of criteria. In addition, growth rates for cells expressing p55c-fgr were restricted, as compared with cells expressing a kinase-deficient protein or cells transformed by proteins with high specific enzymatic activities. Thus, enzymatically active p55c-fgr can simultaneously activate transforming and growth inhibitory pathways.

Differential association of cellular proteins with family protein-tyrosine kinases

We have sought to identify candidate substrates for src family protein-tyrosine kinases potentially important for transformation. Transfected NIH/3T3 cells, each overexpressing a normal or activated version of the fyn, fgr, or src translational product, were examined using antibody to phosphotyrosine as a probe. Expression of each cDNA induced similar but distinct patterns of tyrosine phosphorylated cellular proteins, with the extent of phosphorylation being greatest in cells expressing an activated kinase. A 70-kDa tyrosine-phosphorylated protein was found to associate with the activated fyn gene product. A protein designated p130, tyrosine phosphorylated in vitro, and in vivo, was found to physically associate with the activated product of each src family gene examined. Physical interaction of three different highly transforming tyrosine kinases with a common cellular protein suggests that p130 may play an important role in transformation induced by src family kinases.

Overlapping transcription and termination of the convergent ilvA and ilvY genes of Escherichia coli

The ilvY gene of Escherichia coli is transcribed in a direction opposite to the ilvGMEDA operon, and the translational stop codons of the ilvA and ilvY genes are only 52 base pairs (bp) apart. We have employed galK transcriptional analyses, in vitro transcription assays, and S1 nuclease mapping to show that the converging transcripts of the ilvGMEDA operon and the ilvY gene overlap. The ilvGMEDA transcript terminates at two sites in the distal amino acid coding region of the ilvY gene: a rho-independent termination site 116 bp downstream of the ilvA translational stop codon, ilvA t, and a 62-bp-long rho-dependent termination site, ilvA t', beginning 70 bp beyond the ilvA t site. This tt' termination pattern at the distal end of the ilvGMEDA operon is similar to that of the trp operon of E. coli and the leu operon of Salmonella typhimurium. Termination of ilvY transcription occurs over a broad stretch of DNA several hundred base pairs downstream of the ilvY translational stop codon in the middle of the amino acid coding region of the ilvA gene. These experiments demonstrate that the converging transcripts from the ilvA and ilvY genes terminate in the coding region of the opposing gene.

Rho-dependent transcriptional polarity in the ilvGMEDA operon of wild-type Escherichia coli K12

It has been generally accepted that transcriptional polarity in prokaryotic systems is due to an uncoupling of translation and transcription which unmasks latent rho-dependent termination sites in a polycistronic messenger RNA. In this report, we identify and characterize rho-dependent termination sites responsible for transcriptional polarity in the ilvGMEDA operon of wild-type Escherichia coli K12. The ilvG gene in the wild-type E. coli K12 ilvGMEDA operon contains a frameshift site which results in termination of translation in the middle of the gene. Mutations have been characterized which restore the reading frame of this gene. In addition to allowing full-length expression of the ilvG product, these mutations cause a 3-4-fold elevation in the expression of the operon distal genes. This transcriptional polarity effect on operon distal genes also has been shown to be relieved by rho suppressor mutations. We have used in vitro transcription experiments to identify rho-dependent transcriptional termination sites downstream of the frameshift site in the ilvG gene. Three tandem rho-dependent sites have been located in the ilv'GM' gene region using transcription reactions containing linear or supercoiled plasmid DNA templates. Accumulatively, these rho-dependent termination sites account for about 80% in vitro transcription termination, which is in agreement with the in vivo measurements of transcriptional polarity on operon distal gene expression. These transcriptional experiments provide in vitro confirmation for the latent rho-dependent termination site model of transcriptional polarity.

Selective transfer of individual human chromosomes to recipient cells

Two hypoxanthine phosphoribosyltransferase-deficient human cell lines, D98/AH-2 and HT1080-6TG, were stably transfected with pSV2 gpt, a plasmid containing the selectable marker Escherichia coli xanthine-guanine phosphoribosyl transferase (Eco gpt). Hypoxanthine-aminopterin-thymidine-resistant transformants arose with a frequency of ca. 10(-6) and contained mostly single, but occasionally multiple, copies of the plasmid sequences. These transformants actively express the Eco gpt marker. Single chromosomes from two different HT1080 gpt transformants and one D98 gpt transformant, containing the integrated plasmid sequences, were transferred via microcell-mediated chromosome transfer to hypoxanthine phosphoribosyl transferase-deficient mouse A9 cells. The transferred human chromosomes were identified as 2, 4, and 22, by using a combination of G-11 staining, G-banding, isoenzyme analysis, and in situ hybridization. This system is being used to create a library of interspecies microcell hybrid clones, each clone containing a unique single human chromosome in a mouse background. The complete library will represent the entire human karyotype.